[Haskell-cafe] Type equality proof

Martijn van Steenbergen martijn at van.steenbergen.nl
Tue Mar 17 17:44:28 EDT 2009

Conor McBride wrote:
>> instance Category (:=:) where
>>    id = Refl
>>    Refl . Refl = Refl
> That and the identity-on-objects functor to sets and
> functions.

Not sure what you mean by this, Conor. Can you please express this in 
Haskell code?



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