Who was known for coining the political concept of the 'Social Contract'?

Jean-Jacques Rousseau

Who was Apollo's twin sister, goddess of the hunt? Which Disney film is based on Shakespeare’s "Hamlet"? Which crisp Italian cookie is usually twice-baked and almond flavored? What musical instrument does Jimmy Stewart's character frequently play in "The Shop Around the Corner"? What's an integer called if it's not divisible by 2?