Prove $(p \lor q) \land (\neg p \lor r) \to (q \lor r)$ is a tautology
88104
Prove "$(p \lor q) \land (\neg p \lor r)) \rightarrow (q \lor r)$" is a tautology
139064
Show by using logical connectives laws that $(P\to Q) \land (Q \to R) $ is equivalent to $(P \to R) \land [(P \iff Q) \lor (R \iff Q)]$
142762
how to prove that (P⊃Q)≡(¬Q⊃¬P) ( P ⊃ Q ) ≡ ( ¬ Q ⊃ ¬ P ) is disallowed in intuitionistic logic?
118898
Is there a simple way of proving that $\text{GL}_n(R) \not\cong \text{GL}_m(R)$?
56878
Proof that $a\mid b \land b\mid c \Rightarrow a\mid c $
108367
proving tautologically equivalent
5293
Show that the logic $ \ \forall x \exists y \ P(x,y) \ $ is not logically equivalent to $ \ \exists x \forall y \ P(x,y) \ $
65379
Deriving $\neg R$ from $\{R↔(R∨(P∧¬P)), R↔¬P, ¬P→(P↔(Q→Q)), P→Q\}$
119888
Is it possible to convert $\forall$ quantifiers to $\exists$ quantifiers without negation?
6535
Proof of for-all / there-exists "negation"?
77759
How do i prove that $(p \vee q) \wedge (\neg p \vee r) \rightarrow (q \vee r)$ is a tautology without using the truth table?
113605
In Fitch, how does one prove "(P → Q)" from the premise "(¬P ∨ Q)"?
41223
How to check, whether the formula is a tautology
10540
Prove $\vdash \neg(\square F\land p)$ in $KD$
76347
Shorter proof for some equvalences
49385
Proving $\forall x (A\to B) \to(A \to \forall x B):x\notin \mbox{free}(A)$ in a Hilbert system where it is not an axiom
32027
Given (p ∧ q), use the Fitch system to prove (q ∨ r)