(VAR x y ) (RULES f(x,a(b(y))) -> f(a(a(x)),y) f(x,b(a(y))) -> f(b(b(x)),y) f(a(x),y) -> f(x,a(y)) f(b(x),y) -> f(x,b(y)) ) (COMMENT TRS variant of ab -> aa, ba -> bb )