I'm having trouble with an assignment in Predicate Calculus specifically related to an L-sentence. I need to prove that
$((\forall x (Px \Rightarrow Qx)) \lor(\forall x(Px \Rightarrow \lnot Qx)))$ is not logically valid.
I understand L-structures and in general how to determine their truth value, however I have gone over this question several times and it looks like it should be logically valid, can you show me how it's not?
The question was resolved in the comments. Just adding this note so the question stops showing in lists of unanswered questions.