The circuit shown in the figure has 4 boxes each described by inputs P, Q, R and outputs Y, Zwith Y = P Q R Z = RQ+PR+QP PQ PQ PQ Z R Y PQ Z R Y Y Y Output The circuit acts as a (a) 4 bit ądder giving P + Q (b) 4 bit subtractor giving P-Q (c) 4 bit subtractor giving Q-P (d) 4 bit adder giving P + Q + R Z R Z R [2003 · 2 Markel