(VAR X Y X1 X2 X3) (RULES active(f(X,g(X),Y)) -> mark(f(Y,Y,Y)) active(g(b)) -> mark(c) active(b) -> mark(c) active(g(X)) -> g(active(X)) g(mark(X)) -> mark(g(X)) proper(f(X1,X2,X3)) -> f(proper(X1),proper(X2),proper(X3)) proper(g(X)) -> g(proper(X)) proper(b) -> ok(b) proper(c) -> ok(c) f(ok(X1),ok(X2),ok(X3)) -> ok(f(X1,X2,X3)) g(ok(X)) -> ok(g(X)) top(mark(X)) -> top(proper(X)) top(ok(X)) -> top(active(X)) )