From: Ali Caglayan <alizter@gmail.com>
To: Homotopy Type Theory <HomotopyTypeTheory@googlegroups.com>
Subject: [HoTT] Re: Characteristic Classes for Types
Date: Thu, 27 Sep 2018 17:38:08 -0700 (PDT) [thread overview]
Message-ID: <d48b3ec2-c96d-412c-bb6b-0c3fa0a96586@googlegroups.com> (raw)
In-Reply-To: <91b60f0a-e5e3-4216-a422-9b52bb8a4cc7@googlegroups.com>
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1. This could be possible once a vector bundle has been fully defined. The
idea behind characteristic classes is to classify certain vector bundles
with cohomology. This however may be a bit in the future as, for example,
grassmannians have not yet been defined. Also orthogonal groups are not yet
defined. So it is impossible to say right now if this can be done but it
seems likely.
2. Cohomology in HoTT is not by default singular cohomology like in
algebraic topology. In HoTT we take the definition of cohomology to be the
(truncated) set of maps to an Eilenberg-Maclane space. Concering cohomology
operations, this should definitely be possible. Literature on cohomology
has come out in the last few years so expect more to be written about it.
3. Atiyah-Singer would need quite a lot of work, not to mention the fact it
involves differential structure. Which at the moment it is expected that
differential cohesive HoTT may be able to tackle such a theorem. HoTT on
it's own is quite good at talking about purely homotopical structure. This
is an important point because many topological/manifoldy theorems are not
necesserily homotopical in nature. They may depend on extra structure that
HoTT cannot really describe adequately yet. Take for example Riemann-Roch
which can be considered a special case of Atiyah-Singer. It would need a
good amount of algebraic geometry to be defined and/or proven in order to
state the theorem. Which is unliekly to come around in the next few years.
This doesn't mean it couldn't happen.
Just to show you how underdeveloped cohomology in HoTT is at the moment, an
"elementary" theorem of algebraic topology, the Hurewicz theorem, has not
been proven yet. Though I believe it will be tackled soon.
Types are not topological spaces, they are more literally homotopy types.
This is why I personally, found "the Hodge structure of a type" to be not
within our current viewpoint although Steve Awodey's point about the speed
of the development of HoTT has been considered.
And one final thing: One of the reasons algebraic topologists are exicited
about using and developing HoTT is that it gives a synthetic foundation to
many "purely homotopical" ideas used in algebraic topology that have proofs
and constructions relient on outside ideas or formalisms. This isn't
necesserily a bad thing (look at cobordisms in stable homotopy) however
some simpler areas of the subject should be able to hold their own. (As I
understand).
Therefore it stands to reason that it is unlikely that HoTT will bring
anything new to the table when it comes to the ideas you are talking about.
HoTT essentially provides a synthetic way to reason about homotopy types,
but it isn't an enlightening viewpoint for theorems not homotopic in nature.
And really finally this time: Have a look around at what people are doing
in HoTT at the moment. For example Floris van Doorn's thesis where spectral
sequences for cohomology have been developed in HoTT and formalised in the
Spectral library for the Lean proof assistant. The agda formalisation of
HoTT also usually has a lot of the latest gadgets of snythetic homootpy
theory. Which is a fascinating subject if I do say so myself, but it isn't
algebraic topology. There is a massive intersection but don't take them to
be the same thing.
Anyway if you have read this for congratulations.
Ali Caglayan
On Thursday, 27 September 2018 14:10:09 UTC+1, Juan Ospina wrote:
>
> Recently, there was a post about the Euler characteristic of a type and
> other post about Hodge structure of a type. Then my questions are:
>
> 1) It is possible to construct characteristic classes (Wu,
> Stiefel-Whitney, Chern, Pontryagin classes) for an arbitrary type in
> HoTT?
>
> 2) It is possible to construct singular cohomology for a type and the
> corresponding Steenrod operations?
>
> 3) It is possible to construct an Aityah-Singer index theorem for an
> arbitrary type (a type fibered with other type).
>
> 4) It is possible to construct integrality theores for the characteristic
> numbers of an arbitrary fibered type?
>
>
> Many thanks.
>
> Juan Ospina
> Medellín, Colombia
>
>
>
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next prev parent reply other threads:[~2018-09-28 0:38 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-27 13:10 [HoTT] " Juan Ospina
2018-09-28 0:38 ` Ali Caglayan [this message]
2018-09-28 1:00 ` [HoTT] " Juan Ospina
2018-09-28 1:04 ` Juan Ospina
2018-09-28 2:51 ` Michael Shulman
2018-09-28 5:59 ` [HoTT] the weak infinite groupoid in Simple Type Theory José Manuel Rodriguez Caballero
2018-09-28 19:21 ` Michael Shulman
2018-09-28 20:27 ` José Manuel Rodriguez Caballero
2018-10-01 14:43 ` Michael Shulman
2018-10-01 14:53 ` Steve Awodey
2018-10-01 23:14 ` José Manuel Rodriguez Caballero
2018-10-02 16:20 ` Michael Shulman
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