(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
 a(a(a(x))) -> x
 b(b(b(b(b(b(b(x))))))) -> x
 c(c(c(c(c(c(c(c(c(x))))))))) -> x
 a(b(a(b(x)))) -> x
 b(c(b(c(x)))) -> x
 c(a(c(a(x)))) -> x
 a(b(c(a(b(c(x)))))) -> x
 a(A(x)) -> x
 A(a(x)) -> x
 b(B(x)) -> x
 B(b(x)) -> x
 c(C(x)) -> x
 C(c(x)) -> x
)