(VAR x y z )
(RULES 
        f(x, c(x), c(y)) -> f(y, y, f(y, x, y))
        f(s(x), y, z) -> f(x, s(c(y)), c(z))
        f(c(x), x, y) -> c(y)
        g(x, y) -> x
        g(x, y) -> y
        
)