Existential Pontification and Generalized Abstract Digressions

Elimination rules play an important role in computations over datatypes in proof assistants like Coq. In his paper "Elimination with a Motive", Conor McBride argued that "we should exploit a hypothesis not in terms of its immediate consequences, but in terms of the leverage it exerts on an arbitrary goal: we should give elimination a […]

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So you may have heard about this popular new programming language called Haskell. What's Haskell? Haskell is a non-dependently typed programming language, sporting general recursion, type inference and built-in side-effects. It is true that dependent types are considered an essential component of modern, expressive type systems. However, giving up dependence can result in certain benefits […]

In Software Foundations, equality is defined in this way: Even Coq's equality relation is not built in. It has (roughly) the following inductive definition. Inductive eq0 {X:Type} : X -> X -> Prop := refl_equal0 : forall x, eq0 x x. Why the roughly? Well, as it turns out, Coq defines equality a little differently […]

I spent some of my plane ride yesterday working on Coq versions of the exercises in The HoTT book. I got as far as 1.6 (yeah, not very far, perhaps I should make a GitHub repo if other folks are interested in contributing skeletons. Don't know what to do about the solutions though). All of […]