Determine whether the statement is true or false. If the statement is true, give a proof. If the statement is false, give a counterexample. (Note: the definition of an even integer is an integer that can be expressed as 2k, where k is an integer.) (a) If x and y are both even integers, then x+y is an even integer. (b) If xty is an even integer, then x and y are both even integers