Formal Logic - Natural deduction: Problem with assumptions about exists-negation I'm stuck on how to progress with this proof, despite I have tried, I cannot see the next move.
Given this proof without predicate:

So far what I've accomplished:

My idea is, as I can't see any other option using (-(Sv(P-&gt;Q)) as the first assumption in order to introduce a conditional, so the assumption must end in P ^ -Q ^ -S. As you can see I have obatined -Q and -S but, how do I proof P?
SOLUTION:
It is a bit hard to say exactly which introductions you should perform since we don't have your rule set, but I think the over all strategy should be as follows:
From $\neg (S \lor (P \to Q))$ you get $\neg (P \to Q)$.  Since you have $\neg Q$, you should try to introduce $\neg P$ and thus obtain $P \to Q$.  That should be a contradiction and you can conclude $P$.