import public Decidable.Equality
maybeEq : DecEq a => (x : a) -> (y : a) -> Maybe (x = y)
maybeCong : (f : (a -> b)) -> Maybe (x = y) -> Maybe (f x = f y)
maybeCong2 : (f : (a -> b -> c)) -> Maybe (x = y) -> Maybe (v = w) -> Maybe (f x v = f y w)