premise: A guy surfing in a lake or river while a boat is pulling him. hypothesis: The man is riding a flying surfboard.
contradiction: A man cannot be surfing in a lake and also flying.|contradiction: A man cannot be on a flying surfboard and surfing in a lake at the same time. One is in the air and the other is in the water.|contradiction: If surfing while a boat is pulling him means he is not riding a flying surfboard at the same time.