premise: A man is wearing a neon yellow vest while leaning over a roof and another man is standing behind him. hypothesis: Two men can not see each other because there is a wall in their way.
contradiction: If the man is behind him the he should be able to see him.|contradiction: If one man is standing behind another, he can see the other man.|contradiction: Either one man is standing behind the other or there is a wall in their way, so they can't see each other. Both things cannot be true simultaneously.