0 QTRS
f(0, y) → y f(x, 0) → x f(i(x), y) → i(x) f(f(x, y), z) → f(x, f(y, z)) f(g(x, y), z) → g(f(x, z), f(y, z)) f(1, g(x, y)) → x f(2, g(x, y)) → y