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Re: [Coq-Club] [Agda] Why dependent type theory?


Chronological Thread 
  • From: Sylvain Boulmé <Sylvain.Boulme AT univ-grenoble-alpes.fr>
  • To: coq-club AT inria.fr
  • Subject: Re: [Coq-Club] [Agda] Why dependent type theory?
  • Date: Wed, 4 Mar 2020 10:11:00 +0100
  • Authentication-results: mail3-smtp-sop.national.inria.fr; spf=None smtp.pra=Sylvain.Boulme AT univ-grenoble-alpes.fr; spf=Pass smtp.mailfrom=Sylvain.Boulme AT univ-grenoble-alpes.fr; spf=None smtp.helo=postmaster AT zm-mta-out-3.u-ga.fr

Hello,

My short answer: dependent type theory is a good compromise to formalize "informal reasonings in naive set-theory" with a computer. Because it combines two key-features:
- types are values: you can compute on types and for example, define a family of types indexed by naturals.
- typechecking remains decidable.

If you compare this to untyped set theory (like promoted by Lamport), then membership in set-theory is undecidable, and I do not know whether there is a clear notion of computation in the logic...

Regards,

Sylvain.


Le 03/03/2020 à 23:45, Martin Escardo a écrit :
Dependent types are good for pure mathematics (classical or constructive). They are the natural home to define group, ring, metric space, topological space, poset, lattice, category, etc, and study them. Mathematicians that use(d) dependent types include Voevodsky (in Coq) and Kevin Buzzard (in Lean), among others. Kevin and his team defined, in particular, perfectoid spaces in dependent type theory. Martin

On 03/03/2020 19:43,
jasongross9 AT gmail.com
wrote:
I'm in the process of writing my thesis on proof assistant performance bottlenecks (with a focus on Coq), and there's a large class of performance bottlenecks that come from (mis)using the power of dependent types.  So in writing the introduction, I want to provide some justification for the design decision of using dependent types, rather than, say, set theory or classical logic (as in, e.g., Isabelle/HOL). And the only reasons I can come up with are "it's fun" and "lots of people do it"

So I'm asking these mailing lists: why do we base proof assistants on dependent type theory?  What are the trade-offs involved?
I'm interested both in explanations and arguments given on list, as well as in references to papers that discuss these sorts of choices.

Thanks,
Jason

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