(VAR x y z )
(RULES 
        f(a, g(y)) -> g(g(y))
        f(g(x), a) -> f(x, g(a))
        f(g(x), g(y)) -> h(g(y), x, g(y))
        h(g(x), y, z) -> f(y, h(x, y, z))
        h(a, y, z) -> z
        
)