Thomas Streicher

Thomas Streicher

[Dana Scott]

What sad news!  In past years I many times visited Darmstadt to work with the the group
on Continuous Lattices, and I often visited with Thomas.  In later years his work with the
late Martin Hofmann was very inspiring and fundamental.  A Google Scholar search on
“Streicher Hofmann” turns up many references.  Maybe someone can give a survey
talk on his and their work in one of the up-coming conferences?

        —DANA

Prof. Dana S. Scott
1149 Shattuck Ave
Berkeley, CA 94707
———
Home: (510) 527-5287
Cell: (510) 239-1843



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Re: Thomas Streicher

[Jens Hemelaer]

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I am grateful for getting in touch with Thomas in 2020 through this mailing list. It was wonderful to care about the same problems and then approach them with different methods, and I will miss the joyfulness and passion that came through in his e-mails.

My condolences to his family and friends,
Jens

On Tue, 7 Jan 2025 at 00:01, Peter LeFanu Lumsdaine <p.l.lumsdaine@gmail.com<mailto:p.l.lumsdaine@gmail.com>> wrote:
Very sad news to start the New Year with.  Like others, I was greatly influenced by Thomas’s work — I read his “Semantics” book cover to cover early in my PhD, and have had its meticulous proofs and terrible typography burned into my brain ever since.  As others have noted, he and Martin Hofmann were the first to discover many of the ideas that later grew into homotopy type theory; I first met him (if I remember right) at the 2011 Oberwolfach meeting which brought Voevodsky’s work together with the established “old guard” of type theorists.  Thomas was wonderful to talk maths with over a beer — gruff and opinionated, but always amiable and constructive in his disagreements.  I didn’t see him much since Covid, and am sorry that I never got to discuss more recent developments with him, and now never will.

With condolences to his family and friends,
–Peter.


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Re: Thomas Streicher

[Peter LeFanu Lumsdaine]

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Very sad news to start the New Year with.  Like others, I was greatly influenced by Thomas’s work — I read his “Semantics” book cover to cover early in my PhD, and have had its meticulous proofs and terrible typography burned into my brain ever since.  As others have noted, he and Martin Hofmann were the first to discover many of the ideas that later grew into homotopy type theory; I first met him (if I remember right) at the 2011 Oberwolfach meeting which brought Voevodsky’s work together with the established “old guard” of type theorists.  Thomas was wonderful to talk maths with over a beer — gruff and opinionated, but always amiable and constructive in his disagreements.  I didn’t see him much since Covid, and am sorry that I never got to discuss more recent developments with him, and now never will.

With condolences to his family and friends,
–Peter.


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Re: Thomas Streicher

[Michael Shulman]

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Unfortunately, I had little opportunity to talk with Thomas in person.  But I was blessed to have many email conversations with him, on and off the categories and homotopy type theory mailing lists about type theory, set theory, fibrations, replacement axioms, universes, toposes, and many other topics.  He was always generous with his ideas, insights, and his time, even when I was an undistinguished graduate student -- once he photocopied and sent me by "yellow mail" an unpublished monograph that anticipated something I was working on.  Looking back at some of those emails now, what impresses me is his intellectual courage and honesty: he was never shy about stating and arguing for his opinion, or about asking a question about something he didn't understand, and was always willing to learn as well as to share his own considerable knowledge.  I will miss him, and the community is poorer for his loss.



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Re: Thomas Streicher

[Tom de Jong]

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The first and only time I met Thomas was in September 2019 at the
Workshop on Continuity, Computability, Constructivity (CCC) in
Ljubljana. I was only a first-year PhD student and earlier that year at
TYPES I had felt a little out of place at times, but Thomas immediately
made me feel very comfortable and it was very fun to talk with him. We
made some tentative plans for me to visit him, but unfortunately, and
partly because of the pandemic, I never followed up on these plans.

We are fortunate that Thomas has left us with great expository notes on
categorical logic, and realizability, as well as his book on
domain-theoretic semantics of functional programming, all of which I
have found very useful.

My condolences to his friends and family,
Tom

On 03/01/2025 13:53, Jon Sterling wrote:
> I am so sad to hear this tragic news about Thomas. Thomas was very kind
> and encouraging to me over the years, and made me feel welcome in this
> community; I imagine he had this impact on many other young people
> finding their way. In addition to his momentous scientific contributions
> that I owe my career to, Thomas was also a great conservator of
> important knowledge that might otherwise have been lost had he not
> intervened.
>
> Sincerely,
> Jon
>
>
> On Fri, Jan 3, 2025, at 12:09 PM, Neil Ghani wrote:
>> I'm so gutted. Thomas was an exceptional category theorist but also an
>> exceptional human being. He had a brilliant sense of humour and we
>> loved laughing about the oddities of mathematics.
>>
>> A terrible start to 2025.
>>
>> Neil
>>
>> Sent from Outlook for iOS
>> <https://url.au.m.mimecastprotect.com/s/0ietC5QP8ySZpr2ZMczfvSkM8o5?<https://url.au.m.mimecastprotect.com/s/ixfmC2xMRkUpRkZBDhBi9S5-V_Q?domain=aka.ms>
> domain=aka.ms <https://url.au.m.mimecastprotect.com/s/<https://url.au.m.mimecastprotect.com/s/jlw6C3QNl1SpGm9yrhDs9SQfU6F?domain=url.au.m.mimecastprotect.com>
> Z0QTCmO5wZsjPQMPNhQtWSR3MPW?domain=aka.ms>>
>> *From:* Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
>> *Sent:* Friday, January 3, 2025 11:47 am
>> *To:* categories@mq.edu.au <categories@mq.edu.au>
>> *Cc:* Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
>> *Subject:* Thomas Streicher
>>
>> I just received information that Thomas Streicher passed away yesterday.
>>
>> Thomas fell ill last September, when he could not attend Pino
>> Rosolini's retirement party due to pneumonia; then it turned out he has
>> metastases in the lungs from a pancreatic cancer. After several chemo
>> treatments his situation suddenly worsened, and yesterday he died,
>> peacefully, without pain.
>> Thomas was 66 years old.
>>
>> In Thomas, we mourn a logician and category theorist of exceptional
>> calibre. Let me just recall that in 2011, during an Oberwolfach
>> meeting, Vladimir Voevodsky praised Thomas' work on type theory as a
>> paradigm of precision.
>>
>> But I personally mourn a friend. A warm person with many interests.
>>
>> I wish strength to his wife Eva, and his family.
>>
>> Jaap van Oosten
>>
>>


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Re: Thomas Streicher

[Michael Shulman]

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On Sun, Jan 5, 2025 at 5:54 AM Urs Schreiber <urs.schreiber@googlemail.com<mailto:urs.schreiber@googlemail.com>> wrote:
> Martin Escardo said that Thomas knew about the Univalence axiom before it had a name.

Yes, the idea is essentially the "universe extensionality" in section 5.4 of "The groupoid interpretation of type theory" (83-111 in ISBN:9780198501275<https://url.au.m.mimecastprotect.com/s/F0yFCK1DOrC2B2v1mUMfDS5NaHp?domain=global.oup.com>, pdf<https://url.au.m.mimecastprotect.com/s/URKECL7Eg9fRmRp34Fqh3SyZ3Th?domain=ncatlab.org>), which is where vv will have seen it. Keeping the term "universe extensionality" would have been the right thing to do. The main issue is that the definition of equivalence of types used there is subtly wrong, and vv's contribution really was to fix this part.

To be fair to Martin and Thomas, it's not wrong in the context where they used it, namely a universe of discrete groupoids.  It *would* be wrong if the same definition were also used for higher types.

After the definition of universe extensionality, that paper also contains a prescient definition of what are now called "univalent categories", arguably the best way to formulate category theory in homotopy type theory.



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Re: Thomas Streicher

[Jonathon Funk]

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Yes, very sad news. I knew Thomas from the complete spreads project  (which are a class of geometric morphism).   In particular together (with Marta and Mamuka) we solved the problem of identifying what is complete about complete spreads.  Ultimately, we needed fibrations in order to explain it - Thomas kept us on the straight and narrow.  I loved talking with Thomas about mathematics.  It was in his blood.  I'll never forget the first time we met (nearly 30 years ago) in that pub somewhere in Utrecht:  he came up to me and said: ``Hello, my name is Thomas Streicher''  with such force it nearly bowled me over.  Now that is how to introduce yourself.
So long Thomas, RIP.
Jon



________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Sent: Friday, January 3, 2025 4:04 AM
To: categories@mq.edu.au <categories@mq.edu.au>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Subject: Thomas Streicher


* This email originates from a sender outside of CUNY. Verify the sender before replying or clicking on links and attachments. *

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Benno van den Berg]

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Dear all,


Like so many of you I am deeply saddened by Thomas’ passing.


As part of his position in Darmstadt, he could always hire a PhD or postdoc, and from 2006 - 2011 I was the lucky one. I arrived just after finishing my PhD and through Thomas I discovered many new areas of logic and category theory. I could walk into his office at any time and start talking about anything and before you knew it, hours had passed and we had touched upon anything from mathematics to philosophy, politics, food, literature and life in general.


You got the impression he had studied everything. And not just that, he had also developed his own distinctive opinion about the topic. He would be very fond of unorthodox ideas and would often start a discussion with ``It is probably a complete waste of time, but…’’ and then launch into another fascinating digression.


I start this year with the feeling that I have lost a dear colleague and a dear friend. I will miss his deep knowledge of the areas of mathematics he was so fond of and I came to love as well. I will miss the diners, the drinks and the conversation. I am glad to have been given the opportunity to have spent all these happy times with Thomas, but also very sad to realise these have now come to the end.


I offer my condolences to all his colleagues, friends and family, and especially his wife Eva.


Best wishes,


Benno


Op zo 5 jan 2025 om 14:55 schreef Paul Levy <p.b.levy@bham.ac.uk<mailto:p.b.levy@bham.ac.uk>>:
Correction: it was not Martin Escardo but Steve Awodey who said “He knew about univalence before it was called that.”
Paul

From: Paul Levy <p.b.levy@bham.ac.uk<mailto:p.b.levy@bham.ac.uk>>
Date: Sunday, 5 January 2025 at 00:31
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Subject: Re: Thomas Streicher
This is really sad news.  He was such a great person to talk to and made so many contributions.
Martin Escardo said that Thomas knew about the Univalence axiom before it had a name.  He also was the first to formulate a version of the WISC axiom:
https://ncatlab.org/nlab/show/WISC<https://url.au.m.mimecastprotect.com/s/QrA6Ck815RCOr6QJAH2fjSGPU_c?domain=ncatlab.org>
I would also like to mention his work on control operators, with Martin Hofmann and Bernhard Reus, which I found illuminating in my PhD work.
Paul


From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Date: Friday, 3 January 2025 at 11:49
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher
CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Riba Colin]

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This is a very sad news indeed ...

Like many of us, his patience and generosity provided inestimable
support to me, scientifically and beyond.

I will miss warm and generous discussions. Always frank and sharp,
assuming the best from his interlocutor (or opponent!). Engaged
without quarrelling, and of course ending with some good meal and beer!

I regret not to have visited him since the pandemic...

It provides comfort to me that he meant so much to so many of us!

My deepest condolences to his wife Eva.

Colin


Le 2025-01-03 10:04, Oosten, J. van (Jaap) a écrit :
> I just received information that Thomas Streicher passed away
> yesterday.
> 
>  Thomas fell ill last September, when he could not attend Pino
> Rosolini's retirement party due to pneumonia; then it turned out he
> has metastases in the lungs from a pancreatic cancer. After several
> chemo treatments his situation suddenly worsened, and yesterday he
> died, peacefully, without pain.
>  Thomas was 66 years old.
> 
>  In Thomas, we mourn a logician and category theorist of exceptional
> calibre. Let me just recall that in 2011, during an Oberwolfach
> meeting, Vladimir Voevodsky praised Thomas' work on type theory as a
> paradigm of precision.
> 
>  But I personally mourn a friend. A warm person with many interests.
> 
>  I wish strength to his wife Eva, and his family.
> 
>  Jaap van Oosten
> 
>  		 You're receiving this message because you're a member of the
> Categories mailing list group from Macquarie University. To take part
> in this conversation, reply all to this message.
> 
>  		 View group files [1]   |   Leave group [2]   |   Learn more about
> Microsoft 365 Groups [3]
> 
> 
> 
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> ------
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Re: Thomas Streicher

[Paul Levy]

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Correction: it was not Martin Escardo but Steve Awodey who said “He knew about univalence before it was called that.”
Paul

From: Paul Levy <p.b.levy@bham.ac.uk>
Date: Sunday, 5 January 2025 at 00:31
To: categories@mq.edu.au <categories@mq.edu.au>
Subject: Re: Thomas Streicher
This is really sad news.  He was such a great person to talk to and made so many contributions.
Martin Escardo said that Thomas knew about the Univalence axiom before it had a name.  He also was the first to formulate a version of the WISC axiom:
https://ncatlab.org/nlab/show/WISC<https://url.au.m.mimecastprotect.com/s/f92pCP7L1NfKorgWRSzfxSx8R1v?domain=ncatlab.org>
I would also like to mention his work on control operators, with Martin Hofmann and Bernhard Reus, which I found illuminating in my PhD work.
Paul


From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Date: Friday, 3 January 2025 at 11:49
To: categories@mq.edu.au <categories@mq.edu.au>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Subject: Thomas Streicher
CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Giuseppe Rosolini]

This is very, very sad news. It was expected, but I really hoped he could
recover.

We were very good friends since the fantastic PSSL weekends where we met
regularly.

Thomas was a great mathematician, an especially good one because one could
talk to him, argue even forcibly, but finally agreeing on how to resolve the
argument. And he would suggest to go out for a beer after all that.

We had many common interests, in mathematics and outside mathematics. I was
really sorry he could not be at my retirement party last September. He wrote
to me a few weeks later a very gentle and hopeful message to explain why he
could not attend and was still so incredibly nice, so incredibly Thomas, to
send me the slides he had prepared for the talk, addressing two open
problems in topos theory and explain what he intended to say.

Mathematics was part of his being, and it was a nice mathematics because it
was Thomas's.

His loss is clearly deeply felt by very many. I really miss him!

My sincere condolences go to his wife Eva.

Pino Rosolini



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Re: Thomas Streicher

[Urs Schreiber]

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> Martin Escardo said that Thomas knew about the Univalence axiom before it had a name.

Yes, the idea is essentially the "universe extensionality" in section 5.4 of "The groupoid interpretation of type theory" (83-111 in ISBN:9780198501275<https://url.au.m.mimecastprotect.com/s/E5YBC5QP8ySZxQLoyfzfvSkXpkB?domain=global.oup.com>, pdf<https://url.au.m.mimecastprotect.com/s/2QWyC6XQ68fr1AYERc6hBS5vK3M?domain=ncatlab.org>), which is where vv will have seen it. Keeping the term "universe extensionality" would have been the right thing to do. The main issue is that the definition of equivalence of types used there is subtly wrong, and vv's contribution really was to fix this part.


On Sun, Jan 5, 2025 at 4:31 AM Paul Levy <p.b.levy@bham.ac.uk<mailto:p.b.levy@bham.ac.uk>> wrote:
This is really sad news.  He was such a great person to talk to and made so many contributions.
Martin Escardo said that Thomas knew about the Univalence axiom before it had a name.  He also was the first to formulate a version of the WISC axiom:
https://ncatlab.org/nlab/show/WISC<https://url.au.m.mimecastprotect.com/s/pJxrC71R63CAQx1vrUBiQSoCpwu?domain=ncatlab.org>
I would also like to mention his work on control operators, with Martin Hofmann and Bernhard Reus, which I found illuminating in my PhD work.
Paul


From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Date: Friday, 3 January 2025 at 11:49
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher
CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Dusko Pavlovic]

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Thomas Streicher was honest and patient, and infinitely devoted to the ideas he cared for. Types. He cared for types and he will probably be remembered as long as types are around. Maybe they won't be called types forever, as most ideas get renamed, most writings overwritten, and most names forgotten. But a part of him will live as long as people talk about types in some language because he worked them out so carefully and so honestly. It is not always obvious that honesty is the best strategy, but Thomas demonstrated that it was.

I am struggling what to say and this probably sounds terrible from many angles, but Thomas would understand. His patience made him invincible to most of our nonsense, and I am sure even to cancer.

-- dusko

On Sat, Jan 4, 2025 at 9:43 AM Jonas Frey <jonas743@gmail.com<mailto:jonas743@gmail.com>> wrote:
I'm also very sad that Thomas has left us, and thankful for having known him. Like Jonathan, Thomas was my early mentor, and I learned an incredible amount from the two courses of his that I attended, and by reading pretty much all the other lecture notes on his website (which I still highly recommend to all students) and often knocking on his door to ask questions. At these occasions I experienced his patience and generosity that others have already mentioned. Through Thomas I also got in contact with the category theory and logic community, and found a PhD position with Paul-André Melliès in Paris, all of which has changed my life for the better, and for which I am very thankful. I'm also happy to see that he has touched the lives of so many people, and hope that we can retain some of his spirit and style in this community.

Finally, regarding Thomas' relationship to constructive logic and mathematics, I think his attitude is well summarized by the following quote of his which left a lasting expression on me (though I'm not sure if he was quoting someone else): "Im Krieg, in der Liebe, und auf der Metaebene sind alle Mittel erlaubt".

Jonas


On Sat, 4 Jan 2025 at 16:28, Steven Vickers <s.j.vickers.1@bham.ac.uk<mailto:s.j.vickers.1@bham.ac.uk>> wrote:
Like so many others, I too was sad to learn of Thomas's death.

Martin Escardo, who knew Thomas better than I did, wrote that he was very much against constructive mathematics yet was fond of studying its classical metatheory. That to me was a paradox. Once in our many discussions I remember him pulling me up to explain that he was a logician, not a constructive mathematician. Yet the discussions were fertile. In one, at the Formal Topology workshop in Stockholm, he gave his opinion that defining real exponentiation using a point-free definition of the reals would be too tedious for anyone ever to do it. That's obviously true if you go about it the wrong way (for example, using frame homomorphisms), but it spurred me to thinking how to make the task more tractable, and later my student Ming Ng worked out the details. In our paper we acknowledged Thomas's stimulation.

Steve Vickers.
________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 9:04 AM
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Paul Levy]

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This is really sad news.  He was such a great person to talk to and made so many contributions.
Martin Escardo said that Thomas knew about the Univalence axiom before it had a name.  He also was the first to formulate a version of the WISC axiom:
https://ncatlab.org/nlab/show/WISC<https://url.au.m.mimecastprotect.com/s/HJaoCVARmOHx5L8YPtGfOSEvO8H?domain=ncatlab.org>
I would also like to mention his work on control operators, with Martin Hofmann and Bernhard Reus, which I found illuminating in my PhD work.
Paul


From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Date: Friday, 3 January 2025 at 11:49
To: categories@mq.edu.au <categories@mq.edu.au>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Subject: Thomas Streicher
CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Jonas Frey]

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I'm also very sad that Thomas has left us, and thankful for having known him. Like Jonathan, Thomas was my early mentor, and I learned an incredible amount from the two courses of his that I attended, and by reading pretty much all the other lecture notes on his website (which I still highly recommend to all students) and often knocking on his door to ask questions. At these occasions I experienced his patience and generosity that others have already mentioned. Through Thomas I also got in contact with the category theory and logic community, and found a PhD position with Paul-André Melliès in Paris, all of which has changed my life for the better, and for which I am very thankful. I'm also happy to see that he has touched the lives of so many people, and hope that we can retain some of his spirit and style in this community.

Finally, regarding Thomas' relationship to constructive logic and mathematics, I think his attitude is well summarized by the following quote of his which left a lasting expression on me (though I'm not sure if he was quoting someone else): "Im Krieg, in der Liebe, und auf der Metaebene sind alle Mittel erlaubt".

Jonas


On Sat, 4 Jan 2025 at 16:28, Steven Vickers <s.j.vickers.1@bham.ac.uk<mailto:s.j.vickers.1@bham.ac.uk>> wrote:
Like so many others, I too was sad to learn of Thomas's death.

Martin Escardo, who knew Thomas better than I did, wrote that he was very much against constructive mathematics yet was fond of studying its classical metatheory. That to me was a paradox. Once in our many discussions I remember him pulling me up to explain that he was a logician, not a constructive mathematician. Yet the discussions were fertile. In one, at the Formal Topology workshop in Stockholm, he gave his opinion that defining real exponentiation using a point-free definition of the reals would be too tedious for anyone ever to do it. That's obviously true if you go about it the wrong way (for example, using frame homomorphisms), but it spurred me to thinking how to make the task more tractable, and later my student Ming Ng worked out the details. In our paper we acknowledged Thomas's stimulation.

Steve Vickers.
________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 9:04 AM
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Steven Vickers]

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Like so many others, I too was sad to learn of Thomas's death.

Martin Escardo, who knew Thomas better than I did, wrote that he was very much against constructive mathematics yet was fond of studying its classical metatheory. That to me was a paradox. Once in our many discussions I remember him pulling me up to explain that he was a logician, not a constructive mathematician. Yet the discussions were fertile. In one, at the Formal Topology workshop in Stockholm, he gave his opinion that defining real exponentiation using a point-free definition of the reals would be too tedious for anyone ever to do it. That's obviously true if you go about it the wrong way (for example, using frame homomorphisms), but it spurred me to thinking how to make the task more tractable, and later my student Ming Ng worked out the details. In our paper we acknowledged Thomas's stimulation.

Steve Vickers.
________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Sent: Friday, January 3, 2025 9:04 AM
To: categories@mq.edu.au <categories@mq.edu.au>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Subject: Thomas Streicher

CAUTION: This email originated from outside the organisation. Do not click links or open attachments unless you recognise the sender and know the content is safe.

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Nicolai Kraus]

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That's extremely sad news. It was always a privilege to meet Thomas at conferences and other events. He had an amazing sense of humour and was extremely patient and generous with his time. The influence he had on HoTT (which he wasn't even convinced of) is hard to overestimate. I send my sincere condolences to his family.

 Nicolai



On Fri, Jan 3, 2025 at 11:02 PM Maria Emilia Maietti <maietti@math.unipd.it<mailto:maietti@math.unipd.it>> wrote:

Dear all

I would like to thank life for having met Thomas Streicher and having found in him
a unique expert in solving problems in type theory with categorical methods.


In particular, as a last thing of collaboration, I am very grateful to him for joining us in organizing
the workshop on Doctrines and Fibrations, dedicated to Lawvere, in May 2023 in Padova


https://events.math.unipd.it/WDF2023/#com<https://url.au.m.mimecastprotect.com/s/RR7vC1WLjwsMkDKJ7ULfJSVGtwC?domain=events.math.unipd.it>.


Deep condolences to Eva.


Milly


On 03/01/25 10:04, Oosten, J. van (Jaap) wrote:
I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Maria Emilia Maietti]

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Dear all

I would like to thank life for having met Thomas Streicher and having found in him
a unique expert in solving problems in type theory with categorical methods.


In particular, as a last thing of collaboration, I am very grateful to him for joining us in organizing
the workshop on Doctrines and Fibrations, dedicated to Lawvere, in May 2023 in Padova


https://events.math.unipd.it/WDF2023/#com<https://url.au.m.mimecastprotect.com/s/mKDtC3QNl1Sp9rQP5ugf9SQLYRi?domain=events.math.unipd.it>.


Deep condolences to Eva.


Milly


On 03/01/25 10:04, Oosten, J. van (Jaap) wrote:
I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Jonathan Weinberger]

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Thomas has been my mentor, on from my second semester as an undergraduate in Darmstadt more than 15 years ago, all through the years of a pandemic PhD, and up until these last months. In the summer/fall 2009, shortly after his eager and very warm reply to me cold-emailing him about some questions for references in category theory and the course curriculum, I had the immense pleasure to starting to attend his course cycle on category theory, categorical logic, realizability, and domain theory. His direct style in lectures and conversations were immediately compelling to me. I am grateful for the countless hours in which Thomas taught me (fibered) category theory, type theory, and logic from his unique point of view, always with tireless, joyful enthusiasm. Being such a curious person himself, he taught me to never stop asking questions, be it in mathematics or other aspects of life. When possible, our discussions would lead from his office to a café, and then to a bar. His calm but lively demeanor and very Austrian humor always provided joy and relief, particularly during stressful phases. As an advisor, he would not get tired answering any (repeated) question that I had, and he would always foster my academic autonomy.

I cannot imagine how my academic life would have turned out without such a brilliant, supportive, encouraging, attentive, passionate, generous, patient, funny, and heartfelt mentor such as Thomas.

I am deeply sad for the loss of such an inspiring and dear person for Eva, the community, and anyone who knew or was close to him.

Thomas, I hope you got to see some light in these last dark months. I will miss you forever.

Jonathan

Am Fr., 3. Jan. 2025 um 22:10 Uhr schrieb Robin Cockett <robin@ucalgary.ca<mailto:robin@ucalgary.ca>>:
This is indeed a tragic loss to the category theory community ...

I did not know Thomas Streicher well.  However, I do remember being on a bus with him from Luminy to Marseille and falling  into conversation with him: it left a lasting impression.  It was a bit like falling into a black hole consisting of a unique mixture of humor and totally encyclopedic knowledge.

The bus trip was altogether too short ...

My condolences to his family.

-robin
(Robin Cockett)

________________________________






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Re: Thomas Streicher

[Robin Cockett]

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This is indeed a tragic loss to the category theory community ...

I did not know Thomas Streicher well.  However, I do remember being on a bus with him from Luminy to Marseille and falling  into conversation with him: it left a lasting impression.  It was a bit like falling into a black hole consisting of a unique mixture of humor and totally encyclopedic knowledge.

The bus trip was altogether too short ...

My condolences to his family.

-robin
(Robin Cockett)

________________________________






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Re: Thomas Streicher

[François Lamarche]

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Oh man Oh man.

Thomas was a personal friend and every time he was in Paris we'd make sure to have dinner together.  Most of the times he'd choose the restaurant, except the very last time, when we walked atound the neighborhood of his hotel and picked a swell beer bar in the Butte aux Cailles.  I visited him and Eva several times in Darmstadt and we drove around the countryside,

Right now I'm having flashes of conversations we'd had.

Last time I saw him was a chance meeting on the street.  He was walking back to Gare de l'Est and told me he had time to kill before his train would leave.  One or two days after that last one of those dinners.  So I showed him the neighborhood and we had a beer at a sidewalk café.  It was a sunny day.

I would worry about his health, you know.

RIP Thomas
François
On Friday, January 3rd, 2025 at 10:04 AM, Oosten, J. van (Jaap) <J.vanOosten@uu.nl> wrote:
I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Steve Awodey]

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Dear Jaap and Categories,

I’m deeply saddened by this news, even though we’ve known for some time now that it was probably going to happen soon. Thomas was a great mathematician and a great friend. I met him 30 years ago at the CT in Tours, and we hit it off immediately and remained friends ever since. I visited him in Darmstadt many times, slept on his couch, collaborated on papers, and, in later years, shared students and postdocs. I learned a great deal from him about how to combine type theory and category theory into a single, beautiful subject with fascinating different aspects. He knew about univalence before it was called that, and introduced the Kan simplicial set model of type theory at the workshop in Uppsala in 2006.
He also stood by me when I needed it, without regard to his own interests.  He will be greatly missed.

Steve



On Jan 3, 2025, at 4:04 AM, Oosten, J. van (Jaap) <J.vanOosten@uu.nl> wrote:

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Martin Escardo]

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I met Thomas Streicher, in Darmstadt, when I was a PhD student at Imperial in the last millennium, and then multiple times in mutual visits to Darmstadt, Edinburgh and Birmingham, in addition to many conferences/workshops.


We wrote a couple of papers together. One thing I liked about our interactions is that we never argued, and yet he was very much against constructive mathematics and also HoTT/UF, even though he was fond of studying the (categorical) meta-theory of both.


Since the pandemic started in 2020, we met a number of times by Zoom for virtual pub meetings on Fridays, sometimes only the two of us, and sometimes with guests.


I am glad I had an opportunity to meet him by Zoom for half an hour a week before Christmas. He knew his fate, but otherwise it was just as usual, with him asking, in particular, how a student he sent to Birmingham is doing, and then telling me what he was thinking about in mathematics, and asking me what I was doing.


Thomas was a great friend for about 30 years, and I will miss him forever.


I am so sad.


M.


On 03/01/2025 09:04, Oosten, J. van (Jaap) wrote:
I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Steve Awodey]

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Re: Thomas Streicher

[Valeria de Paiva]

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What sad news! Thomas was a very good friend. He was not one for big hugs or other effusiveness, but someone to count on and trust.
I will miss him dearly, and I wish I had shown more affection when I last saw him in the meeting celebrating Bill Lawvere. Thomas could be pretty intimidating because of the abilities mentioned by others, but once you got over that, he was a lovely teddy bear-like friend. My sentiments to his family and friends. Thank you, Jaap, for conveying the bad news.
Valeria

On Fri, Jan 3, 2025 at 8:45 AM Graham White <g.graham.white@gmail.com<mailto:g.graham.white@gmail.com>> wrote:
Such a loss.

Graham

On Fri, Jan 3, 2025 at 3:42 PM Joyal, André <joyal.andre@uqam.ca<mailto:joyal.andre@uqam.ca>> wrote:
Dear Jaap,

I was not closed to Thomas Streicher but I remember a warm person with
a great passion for logic and category theory.
His work with Martin Hofmann on the groupoid model of Martin-Lof type theory was a precursor
of the homotopy models of Awodey-Warren and Voevodsky.
He took seriously the work of Benabou on fibered categories and he
applied it successfully to type theory.
Jonathan Weinberger, his last student, has great contributions to simplicial homotopy theory.

We will miss him.

André Joyal

________________________________
De : Bernhard Reus <bernhard@sussex.ac.uk<mailto:bernhard@sussex.ac.uk>>
Envoyé : 3 janvier 2025 09:36
À : Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>; categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Objet : Re: Thomas Streicher

Thomas was not only a brilliant type theorist, category theorist and mathematician, as many already pointed out, he was also very generous with his time, happy to discuss any topic he was interested in. He was like a walking lexicon.

I am devastated.

It was him who introduced me to type theory and constructivism, changing the course of my PhD, eventually co-supervising it. Thomas had a massive impact on my life, more than he will ever know now.  I am immensely grateful to have had the privilege to work with him. It was great fun writing papers with him, then afterwards going for a nice meal. Those were good times, back then in Passau and Munich in the 90es.

As a PhD student, I remember going into his office to ask a question, coming out, hours later, with many new questions to think about. Amazed and bedazzled by what I just heard.
His great sense of humour and passion for the subject was second to none. At conferences, there were always colleagues queueing to have a chat with him.  When they made Thomas, they broke the mould.

Like Jaap, I mourn a great friend.
My heart goes out to Eva, his wife, and all his friends and family.

Bernhard




________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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--
Graham White
London


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Re: Thomas Streicher

[Kurz, Alexander]

Thomas was the inspiration why I took up category theory when I started my PhD. I had not encountered CT before. I started my PhD on modal and temporal logic, moving from the TU Munich to the LMU, which is where I met Thomas as he was still at the LMU at the chair of Martin Wirsing at the time, working with Bernhard Reus. This was in 1995.

A highlight I remember well, in April 1999, we organized a Spring School in Munich where Thomas lectured on Fibered Categories (and Giuseppe Rosolini on Sheaves and Martin Hyland on Categorical Logic and Type Theory).

Over the years, every now and then, I had a question on CT and Thomas always took the time to explain everything. He once even added sth to his notes on fibred category as an answer.

Last time I met him was less than a year ago on zoom and I still remember vividly the inspiration and energy I got from talking to him.

My thoughts go to all who have been much closer to Thomas than me.

Alexander



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Re: Thomas Streicher

[Sergei Soloviev]

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Deep regrets! He was great in our domain, in maths in general, and his humanity was remarkable...

Sergei Soloviev



Le Vendredi, Janvier 03, 2025 10:04 CET, "Oosten, J. van (Jaap)" <J.vanOosten@uu.nl> a écrit:

> I just received information that Thomas Streicher passed away yesterday.
> 
> Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
> Thomas was 66 years old.
> 
> In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.
> 
> But I personally mourn a friend. A warm person with many interests.
> 
> I wish strength to his wife Eva, and his family.
> 
> Jaap van Oosten
> 
> 
> 
> You're receiving this message because you're a member of the Categories mailing list group from Macquarie University. To take part in this conversation, reply all to this message.
> 
> View group files<https://url.au.m.mimecastprotect.com/s/sUINCxngGkf1RWNgQS8fgSyp2HK?domain=outlook.office365.com>   |   Leave group<https://url.au.m.mimecastprotect.com/s/xHUgCyoj8Pur2BVQyUMhySx_JJn?domain=outlook.office365.com>   |   Learn more about Microsoft 365 Groups<https://url.au.m.mimecastprotect.com/s/h3zCCzvkmpfMwjVymtgioS9qRk-?domain=aka.ms>
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Re: Thomas Streicher

[Graham White]

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Such a loss.

Graham

On Fri, Jan 3, 2025 at 3:42 PM Joyal, André <joyal.andre@uqam.ca<mailto:joyal.andre@uqam.ca>> wrote:
Dear Jaap,

I was not closed to Thomas Streicher but I remember a warm person with
a great passion for logic and category theory.
His work with Martin Hofmann on the groupoid model of Martin-Lof type theory was a precursor
of the homotopy models of Awodey-Warren and Voevodsky.
He took seriously the work of Benabou on fibered categories and he
applied it successfully to type theory.
Jonathan Weinberger, his last student, has great contributions to simplicial homotopy theory.

We will miss him.

André Joyal

________________________________
De : Bernhard Reus <bernhard@sussex.ac.uk<mailto:bernhard@sussex.ac.uk>>
Envoyé : 3 janvier 2025 09:36
À : Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>; categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Objet : Re: Thomas Streicher

Thomas was not only a brilliant type theorist, category theorist and mathematician, as many already pointed out, he was also very generous with his time, happy to discuss any topic he was interested in. He was like a walking lexicon.

I am devastated.

It was him who introduced me to type theory and constructivism, changing the course of my PhD, eventually co-supervising it. Thomas had a massive impact on my life, more than he will ever know now.  I am immensely grateful to have had the privilege to work with him. It was great fun writing papers with him, then afterwards going for a nice meal. Those were good times, back then in Passau and Munich in the 90es.

As a PhD student, I remember going into his office to ask a question, coming out, hours later, with many new questions to think about. Amazed and bedazzled by what I just heard.
His great sense of humour and passion for the subject was second to none. At conferences, there were always colleagues queueing to have a chat with him.  When they made Thomas, they broke the mould.

Like Jaap, I mourn a great friend.
My heart goes out to Eva, his wife, and all his friends and family.

Bernhard




________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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--
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London


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Re: Thomas Streicher

[Joyal, André]

[-- Attachment #1: Type: text/plain, Size: 4227 bytes --]

Dear Jaap,

I was not closed to Thomas Streicher but I remember a warm person with
a great passion for logic and category theory.
His work with Martin Hofmann on the groupoid model of Martin-Lof type theory was a precursor
of the homotopy models of Awodey-Warren and Voevodsky.
He took seriously the work of Benabou on fibered categories and he
applied it successfully to type theory.
Jonathan Weinberger, his last student, has great contributions to simplicial homotopy theory.

We will miss him.

André Joyal

________________________________
De : Bernhard Reus <bernhard@sussex.ac.uk>
Envoyé : 3 janvier 2025 09:36
À : Oosten, J. van (Jaap) <J.vanOosten@uu.nl>; categories@mq.edu.au <categories@mq.edu.au>
Objet : Re: Thomas Streicher

Thomas was not only a brilliant type theorist, category theorist and mathematician, as many already pointed out, he was also very generous with his time, happy to discuss any topic he was interested in. He was like a walking lexicon.

I am devastated.

It was him who introduced me to type theory and constructivism, changing the course of my PhD, eventually co-supervising it. Thomas had a massive impact on my life, more than he will ever know now.  I am immensely grateful to have had the privilege to work with him. It was great fun writing papers with him, then afterwards going for a nice meal. Those were good times, back then in Passau and Munich in the 90es.

As a PhD student, I remember going into his office to ask a question, coming out, hours later, with many new questions to think about. Amazed and bedazzled by what I just heard.
His great sense of humour and passion for the subject was second to none. At conferences, there were always colleagues queueing to have a chat with him.  When they made Thomas, they broke the mould.

Like Jaap, I mourn a great friend.
My heart goes out to Eva, his wife, and all his friends and family.

Bernhard




________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Henning Basold]

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I am incredibly saddened by the passing of Thomas. As others have already stated: Thomas was a very kind, generous and brilliant person. His work is of greatest importance to many of us here, as was his personality and human spirit. The few times I met Thomas are still strongly present in my memory. We had good discussions on mathematical, societal and philosophical topics, and also continued those over some good beer.

Thomas will be sorely missed. I wish strength to Eva and Thomas' family in these difficult times. My thoughts are with you.

Henning

On 03/01/2025 15:36, Bernhard Reus wrote:
Thomas was not only a brilliant type theorist, category theorist and mathematician, as many already pointed out, he was also very generous with his time, happy to discuss any topic he was interested in. He was like a walking lexicon.

I am devastated.

It was him who introduced me to type theory and constructivism, changing the course of my PhD, eventually co-supervising it. Thomas had a massive impact on my life, more than he will ever know now.  I am immensely grateful to have had the privilege to work with him. It was great fun writing papers with him, then afterwards going for a nice meal. Those were good times, back then in Passau and Munich in the 90es.

As a PhD student, I remember going into his office to ask a question, coming out, hours later, with many new questions to think about. Amazed and bedazzled by what I just heard.
His great sense of humour and passion for the subject was second to none. At conferences, there were always colleagues queueing to have a chat with him.  When they made Thomas, they broke the mould.

Like Jaap, I mourn a great friend.
My heart goes out to Eva, his wife, and all his friends and family.

Bernhard




________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Bernhard Reus]

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Thomas was not only a brilliant type theorist, category theorist and mathematician, as many already pointed out, he was also very generous with his time, happy to discuss any topic he was interested in. He was like a walking lexicon.

I am devastated.

It was him who introduced me to type theory and constructivism, changing the course of my PhD, eventually co-supervising it. Thomas had a massive impact on my life, more than he will ever know now.  I am immensely grateful to have had the privilege to work with him. It was great fun writing papers with him, then afterwards going for a nice meal. Those were good times, back then in Passau and Munich in the 90es.

As a PhD student, I remember going into his office to ask a question, coming out, hours later, with many new questions to think about. Amazed and bedazzled by what I just heard.
His great sense of humour and passion for the subject was second to none. At conferences, there were always colleagues queueing to have a chat with him.  When they made Thomas, they broke the mould.

Like Jaap, I mourn a great friend.
My heart goes out to Eva, his wife, and all his friends and family.

Bernhard




________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Jelle Herold]

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FWIW: Seeing just his name the subject, felt like a punch in the stomach... Thomas was something else. Many years ago while I was a student, studying topology and depedent type theory, Vladimir Voevodsky dropped the first versions of univalent foundations code and I immediately started playing around with this and emailed VV. This led to "discovering" Thomas' work and later I had the blessing to meet Thomas in person. We spoke extensively about all kinds of topics. What Neil said: such a sharp, funny person, he was extremely generous with his time and insights and he didn't judge (my lack of credentials). He held some incredibly deep views and was decades ahead of others. These conversations were very inspiring and meaningful to me and always stuck... Massive loss :-(

On Fri, Jan 3, 2025, 1:11 PM Neil Ghani <neil.ghani@strath.ac.uk<mailto:neil.ghani@strath.ac.uk>> wrote:
I'm so gutted. Thomas was an exceptional category theorist but also an exceptional human being. He had a brilliant sense of humour and we loved laughing about the oddities of mathematics.

A terrible start to 2025.

Neil

Sent from Outlook for iOS<https://url.au.m.mimecastprotect.com/s/9BhACwV1jpSGVwNB9tVfPSJVTGt?domain=aka.ms>
________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au<mailto:categories@mq.edu.au> <categories@mq.edu.au<mailto:categories@mq.edu.au>>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Jon Sterling]

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I am so sad to hear this tragic news about Thomas. Thomas was very kind and encouraging to me over the years, and made me feel welcome in this community; I imagine he had this impact on many other young people finding their way. In addition to his momentous scientific contributions that I owe my career to, Thomas was also a great conservator of important knowledge that might otherwise have been lost had he not intervened.

Sincerely,
Jon


On Fri, Jan 3, 2025, at 12:09 PM, Neil Ghani wrote:
> I'm so gutted. Thomas was an exceptional category theorist but also an 
> exceptional human being. He had a brilliant sense of humour and we 
> loved laughing about the oddities of mathematics.
>
> A terrible start to 2025. 
>
> Neil 
>
> Sent from Outlook for iOS 
> <https://url.au.m.mimecastprotect.com/s/G0mJCgZ05JfAwzBwZiNfnS4leO5?domain=aka.ms>
> *From:* Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
> *Sent:* Friday, January 3, 2025 11:47 am
> *To:* categories@mq.edu.au <categories@mq.edu.au>
> *Cc:* Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
> *Subject:* Thomas Streicher 
> 
> I just received information that Thomas Streicher passed away yesterday.
>
> Thomas fell ill last September, when he could not attend Pino 
> Rosolini's retirement party due to pneumonia; then it turned out he has 
> metastases in the lungs from a pancreatic cancer. After several chemo 
> treatments his situation suddenly worsened, and yesterday he died, 
> peacefully, without pain.
> Thomas was 66 years old.
>
> In Thomas, we mourn a logician and category theorist of exceptional 
> calibre. Let me just recall that in 2011, during an Oberwolfach 
> meeting, Vladimir Voevodsky praised Thomas' work on type theory as a 
> paradigm of precision.
>
> But I personally mourn a friend. A warm person with many interests.
>
> I wish strength to his wife Eva, and his family.
>
> Jaap van Oosten
>
> 
> 
> You're receiving this message because you're a member of the Categories 
> mailing list group from Macquarie University. To take part in this 
> conversation, reply all to this message. 
> 
> View group files 
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Re: Thomas Streicher

[Neil Ghani]

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I'm so gutted. Thomas was an exceptional category theorist but also an exceptional human being. He had a brilliant sense of humour and we loved laughing about the oddities of mathematics.

A terrible start to 2025.

Neil

Sent from Outlook for iOS<https://url.au.m.mimecastprotect.com/s/0ietC5QP8ySZpr2ZMczfvSkM8o5?domain=aka.ms>
________________________________
From: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Sent: Friday, January 3, 2025 11:47 am
To: categories@mq.edu.au <categories@mq.edu.au>
Cc: Oosten, J. van (Jaap) <J.vanOosten@uu.nl>
Subject: Thomas Streicher

I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Re: Thomas Streicher

[Siyabonga Mthimkulu]

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Although I never met him in person, we exchanged communication around September. During our conversations, he was so kind! I was inspired by how he wrote mathematics, particularly his notes on category theory. May his soul rest in eternal peace.

[https://ci3.googleusercontent.com/mail-sig/AIorK4yxMRS3yXcOoSH7tDGQ1RFTkzQUFXq7ecKO-2gwNCtBGlGLuv7UHFRv5G9W5BhOirB1CY4hfyd-w7X_]
Siyabonga  Mthimkulu
Heidelberg Laureate Forum Alumni
Ph.D Student, Double Categories
African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg 7945, Cape Town, South Africa.
________________________________________________________________________
"Ad Eundum Quo Nemo Ante Iit." — Star Trek
________________________________________________________________________

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On Fri, Jan 3, 2025 at 1:46 PM Oosten, J. van (Jaap) <J.vanOosten@uu.nl<mailto:J.vanOosten@uu.nl>> wrote:
I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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Thomas Streicher

[Oosten, J. van (Jaap)]

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I just received information that Thomas Streicher passed away yesterday.

Thomas fell ill last September, when he could not attend Pino Rosolini's retirement party due to pneumonia; then it turned out he has metastases in the lungs from a pancreatic cancer. After several chemo treatments his situation suddenly worsened, and yesterday he died, peacefully, without pain.
Thomas was 66 years old.

In Thomas, we mourn a logician and category theorist of exceptional calibre. Let me just recall that in 2011, during an Oberwolfach meeting, Vladimir Voevodsky praised Thomas' work on type theory as a paradigm of precision.

But I personally mourn a friend. A warm person with many interests.

I wish strength to his wife Eva, and his family.

Jaap van Oosten



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