A nice intro/showcase to Coq, I suppose. But the triviality of this frankly makes it difficult for me to understand what value this has and what it teaches us - we've just proven that one kind of syntax is equivalent to another, because of an intuitionistic tautology. What I'd like to know is what it would mean for the rust type system if this weren't true, and therefore, what is really the difference between rust opaque types and generics in function signatures other than syntactic, and their formulation?