(VAR x y z )
(RULES 
        t(f(x),g(y),f(z)) -> t(z,g(x),g(y))
        t(g(x),g(y),f(z)) -> t(f(y),f(z),x)
        f(g(x)) ->= g(f(x))
        g(f(x)) ->= f(g(x))
        f(f(x)) ->= g(g(x))
        g(g(x)) ->= f(f(x))
)