Uniqueness of equilibrium Gross substitutes: two goods i andj are gross substitutes at price p, if 0z,(p) ≥0fori≠j Proposition: If all goods are gross substitutes at all price, then if p is an equilibrium price, then it's the unique equilibrium priceUniqueness of equilibrium • Gross substitutes: two goods i and j are gross substitutes at price p, if : • Proposition: If all goods are gross substitutes at all price, then if p * is an equilibrium price, then it’s the unique equilibrium price. ( ) 0 for j i z i j p     p