I missed a step: contramap :: (a -> b) -> Op c b -> Op c a -- substitute Contravariant f for the Op instance, c is introduced as a new type variable contr

I missed a step: contramap :: (a -> b) -> Op c b -> Op c a -- substitute Contravariant f for the Op instance, c is introduced as a new type variable contramap :: (a -> b) -> (b -> c) -> (a -> c)