P2.1.6 Let P(x, y) be a binary predicate where the type of z is A and the type of y is B. We define the projection ri(P) to be the unary predicate on A defined as follows: Pis true if and only if there exists an element y of B such that P(x,y) is true. Similarly, 2(P) is the unary predicate on B defined so that 2 (P)(I) is true if and only if there exists an elem ent r of A such that P(x, y) is true. ows: (a) Let A = B = {0, 1, 2, 3} and define P(z, y) to mean "z