0 QTRS
p(0) → 0 p(s(X)) → X leq(0, Y) → true leq(s(X), 0) → false leq(s(X), s(Y)) → leq(X, Y) if(true, X, Y) → X if(false, X, Y) → Y diff(X, Y) → if(leq(X, Y), 0, s(diff(p(X), Y)))