(VAR X X1 X2 Y ) (RULES f(g(X), Y) -> f(X, n__f(n__g(X), activate(Y))) f(X1, X2) -> n__f(X1, X2) g(X) -> n__g(X) activate(n__f(X1, X2)) -> f(activate(X1), X2) activate(n__g(X)) -> g(activate(X)) activate(X) -> X )