Some values for Ackermann's function:

             n            m            ACK(n m)
            -------------------------------------------------------
             1            1              3
             1            2              4
             2            1              5
             2            2              7 
             2            3              9
             3            2              29
             3            3              61
             3            4            stack overflow

			ack(0,M,R):- R is M+1,!.
             ack(N,0,R):- R1 is N-1,ack(R1,1,R).
             ack(N,m,R):- N1 is N-1,M1 is M-1,ack(N,M1,R1),ack(N1,R1,R).