Prove using natural deduction that $(R \rightarrow (P \rightarrow Q))\vdash (Q\rightarrow P) \lor (P \rightarrow Q)$
9282
Prove using natural deduction $((P \land Q) \rightarrow R) \vdash (P \rightarrow R) \lor (Q\rightarrow R)$
48614
Why is "$P \Rightarrow Q$" equivalent to "$\neg Q \Rightarrow \neg P$"?
10598
Contrapositive Fitch Proof
65379
Deriving $\neg R$ from $\{R↔(R∨(P∧¬P)), R↔¬P, ¬P→(P↔(Q→Q)), P→Q\}$
133884
A proof using Yoneda lemma
116978
Trying to prove $p,p \to (r \to q) \vdash (\neg q \to \neg r)$ by using natural deduction.
10540
Prove $\vdash \neg(\square F\land p)$ in $KD$
91861
Propositional Logic: p → q, ¬p → r, ¬q → ¬r ⊢ q
124424
How to show that there is a deduction of $\varphi\leftrightarrow\psi$
50273
How to prove $\lvert \lVert x \rVert - \lVert y \rVert \rvert \overset{\heartsuit}{\leq} \lVert x-y \rVert$?
79407
How to solve ~(P → Q) : P & ~Q by natural deduction?
67483
Show that $|a-b|<\epsilon \Rightarrow |a|<|b|+\epsilon$
111862
Proof for sequent (Logic)
47161
Quick logic question about $P\leftrightarrow Q$, terminology
15354
Formal proof of $\exists x \forall y P(x,y) \implies \forall y \exists x P(x,y)$
578
In classical logic, why is $(p\Rightarrow q)$ True if both $p$ and $q$ are False?
34768
Proving $(p \oplus q) \oplus r=p \oplus (q \oplus r)$