MAYBE
235.10/60.29	MAYBE
235.10/60.29	
235.10/60.29	Problem:
235.10/60.29	 active(f(X,X)) -> mark(f(a(),b()))
235.10/60.29	 active(b()) -> mark(a())
235.10/60.29	 active(f(X1,X2)) -> f(active(X1),X2)
235.10/60.29	 f(mark(X1),X2) -> mark(f(X1,X2))
235.10/60.29	 proper(f(X1,X2)) -> f(proper(X1),proper(X2))
235.10/60.29	 proper(a()) -> ok(a())
235.10/60.29	 proper(b()) -> ok(b())
235.10/60.29	 f(ok(X1),ok(X2)) -> ok(f(X1,X2))
235.10/60.29	 top(mark(X)) -> top(proper(X))
235.10/60.29	 top(ok(X)) -> top(active(X))
235.10/60.29	
235.10/60.29	Proof:
235.10/60.29	 Open
235.10/60.30	EOF