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