(VAR X X1 X2) (RULES active(h(X)) -> mark(g(X,X)) active(g(a,X)) -> mark(f(b,X)) active(f(X,X)) -> mark(h(a)) active(a) -> mark(b) active(h(X)) -> h(active(X)) active(g(X1,X2)) -> g(active(X1),X2) active(f(X1,X2)) -> f(active(X1),X2) h(mark(X)) -> mark(h(X)) g(mark(X1),X2) -> mark(g(X1,X2)) f(mark(X1),X2) -> mark(f(X1,X2)) proper(h(X)) -> h(proper(X)) proper(g(X1,X2)) -> g(proper(X1),proper(X2)) proper(a) -> ok(a) proper(f(X1,X2)) -> f(proper(X1),proper(X2)) proper(b) -> ok(b) h(ok(X)) -> ok(h(X)) g(ok(X1),ok(X2)) -> ok(g(X1,X2)) f(ok(X1),ok(X2)) -> ok(f(X1,X2)) top(mark(X)) -> top(proper(X)) top(ok(X)) -> top(active(X)) )