Am 22.12.20 um 11:40 schrieb Oleg Grenrus:
I didn't want to clash with Prelude names. Also in Heyting-generality "not" is not correct either. (In general, neg is not involutive).
Yes, obviously. I still think a class Boolean for boolean algebras (with the usual operators now limited to Bool) would be nice. I don't care too much whether it has HeytingAlgebra as super class or not, since I have never had any use for the more general classes. I think I mentioned in the beginning that my main motivation is convenience. Predicates are ubiquitous in programming and the desire to combine them using generalized boolean operators crops up almost everywhere. It amazes me how the designers of Haskell included this elaborate hierarchy of types and classes for all sorts of numbers in the standard libraries, but apparently never thought of generalizing booleans to predicates (and other boolean algebras). Cheers Ben