0 QTRS
p(0) → 0 p(s(x)) → x le(0, y) → true le(s(x), 0) → false le(s(x), s(y)) → le(x, y) minus(x, y) → if(le(x, y), x, y) if(true, x, y) → 0 if(false, x, y) → s(minus(p(x), y))