\f24. Find the mistake in the "proof" of the following "proposition." Is this "proposition" true? If not, find a counterexample. "Proposition." Let A, B and C be sets and suppose that AC BUC . Then AC Bor ACC. "proof. " Let x be any object and suppose that . A. Then xe BUC since Ac BUC. Thus, by the definition of union, xe Bor xeC. Therefore, for all objects x, if x e A, then x e Bor, for all objects x, if x EA, then x EC. Hence, by the definition of subset, Ac Bor ACC