(VAR x y z)
(RULES
 f(x,f(y,z)) ->  f(f(x,y),z)
 f(x,i(x)) -> e
 f(i(x), x) -> e
 f(e, x) -> x
 f(x,e) ->  x
 T(r(t(R(R(x))))) -> x
 R(s(r(S(S(x))))) -> x
 S(t(s(T(T(x))))) -> x
 r(R(x)) -> x
 R(r(x)) -> x
 s(S(x)) -> x
 S(s(x)) -> x
 t(T(x)) -> x
 T(t(x)) -> x
)