(VAR x y z )
(RULES 
        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
        
)