Susan does not go on a diet and is diligent.
All young adults go on a diet. All college students are young adults. All Yale students are college students. Someone is either a Yale student or a Harvard student. All Harvard students are diligent. If Susan is a Harvard student, then she is a young adult. If Susan is a Yale student, then she does not go on a diet.
∀x (YoungAdult(x) → GoOnDiet(x)) ∀x (CollegeStudent(x) → YoungAdult(x)) ∀x (YaleStudent(x) → CollegeStudent(x)) ∀x (YaleStudent(x) ∨ HarvardStudent(x)) ∀x (HarvardStudent(x) → Diligent(x)) HarvardStudent(susan) → YoungAdult(susan) YaleStudent(susan) → ¬GoOnDiet(susan)