2. For all sets X, Y and Z, prove the given statements by the indicated method. (14 points, 7 each)
(a). Method of element argument: If $X \cap Y \subseteq Z$, then $(X - Z) \cap (Y - Z) = \Phi$, where $\Phi$ denotes the empty set.
(b). Method of algebra (cite properties used for every step): If $X \Delta Y = (X - Y) \cup (Y - X)$, then $(X \Delta Y) \cup Y = X \cup Y$.
