From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
From: "Thomas Bushnell, BSG" <tb+usenet@becket.net>
Message-ID: <87it9ruy4s.fsf@becket.becket.net>
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References: <87k7u7r7jl.fsf@becket.becket.net>, <200201242140.QAA12470@math.psu.edu>
Subject: Re: [9fans] Getting started in Plan9 - help
Date: Fri, 25 Jan 2002 10:00:32 +0000
Topicbox-Message-UUID: 44dcb0ba-eaca-11e9-9e20-41e7f4b1d025

cross@math.psu.edu (Dan Cross) writes:

> > To delete n characters, obviously, you sound BS^n DEL^n, and certainly
> > not (BS DEL)^n.
>
> I think you mean BS * n followed by DEL * n.  You want repitition, not
> exponentiation (which would be meaningless, I think).  The operation in
> this context is non-distributive, though.

In formal languages theory, "product" is usually concatenation,
"exponentiation" is repeated concatenation.  (For example, one says
that a DFA can scan A^n but not A^n B^n; one says that a context free
grammar can parse A^n B^n but not A^n B^n C^n.)

Your notation would have "addition" to be concatenation, and "product"
to be repeated concatenation.  That convention would work as well, but
since addition is conventionally always commutative, and product is
not, it's a more confusing convention.  (As you note, it suggests a
distributive property which of course does not exist.)

In other words, we agree about substance but are just using different
notations.

> > There may have been additional meanings to DEL, but the only one I
> > know of is as part of a BS DEL sequenc.e.
>
> Is this one of those, ``well, people are still posting about this
> subject, therefore I feel no need to worry about its topicality...''
> things?

Of course.  :)  Plus I think it's fun.

> Surely there are more important things to worry about, like getting
> the Atari 2600 simulator working....

Well, or getting Plan 9 to boot on my laptop.