Let X and Y be random variables on a probability space (12,F,P) and let A F. Assume that X and Y both only take the values 1 and -1 and define Z: 2 R by X( WY (W) if we A Z(w) if we AC ={XW) Let V be the set containing all values Z can take. a) For all u V, show that Su = Z-'{u} F