I have read that the powerset constuction when viewed as an endofunctor is contravariant but I cant find any explanation of why it is contravariant and not covariant. Any clues?
ie: if f is an arrow A->B why is the arrow P(f) an arrow PB->PA
I did wonder if the author was saying if you view it as contravariant as opposed to covariant then various other things follow. So is it necessarily contravariant?