premise: A young adult is doing a back flip on a trampoline near a lake. hypothesis: A child jumps into the lake.
contradiction: The subject is either a young adult or a child, it cannot be both. A young adult implies that the subject is in their 20s whereas a child would be much younger than that. Doing a back flip on a trampoline near a lake requires the subject to be on the trampoline, whereas jumping into the lake would require the participant to be in the water.