(VAR x x' ) (RULES a(a(x)) -> b(c(x)) b(c(x)) -> a(b(x)) b(a(x)) -> a(a(x)) c(c(x)) -> a(a(x)) c(a(x)) -> c(a(x)) a(a(x)) -> a(a(x)) c(b(x)) -> a(b(x)) b(b(x)) -> b(a(x)) a(c(x)) -> c(b(x)) c(a(b(x'))) -> a(b(c(x'))) b(b(a(x'))) -> b(a(b(x'))) b(c(b(x'))) -> a(a(c(x'))) c(a(a(x'))) -> a(b(a(x'))) )