Better termination for s(X)-sum

Question

(Let me sneak that in within the wave of midterm questions.)

A common definition for the sum of two natural numbers is nat_nat_sum/3:

na         


        

Answer 1

The obvious trick is to flip the arguments:

sum(0,N,N).
sum(N,0,N).
sum(s(A),B,s(C)):- sum(B,A,C) ; sum(A,B,C).