premise: A researcher is evaluating exactly four medicines: W, X, Y, and Z. The only side effects the medicines can have are fatigue, headaches, palpitations, and sweating. The researcher knows the following to be true of the medicines side effects: Each medicine has at least one side effect. No medicine has both fatigue and palpitations as side effects. Medicine Z has no side effect in common with any of the other medicines. Medicines W and X have exactly one side effect in common. Fatigue is a side effect of medicine W. Palpitations are a side effect of medicine X. Sweating is not a side effect of medicine Y. If sweating is not a side effect of medicine Z, then which one of the following statements must be true?
hypothesis: Headaches are a side effect of medicine Y.