How to proof "(𝑃∧𝑄)→¬(¬𝑃∨¬𝑄)" is a tautology
127733
How to prove De Morgan’s laws without using contradictions
40048
Finding the fallacy in this broken proof
36942
What does it mean that a set S tautologically implies wff $\tau$
77160
How to prove the cosets are distinct?
117431
Are the proofs for the properties of parallel lines, and that a triangle has 180 degrees, inherently tautological?
93410
How to prove ~ (~P & ~Q) : P ∨ Q by natural deduction
135694
Proving $\kappa^{\lambda} = |\{X: X \subseteq \kappa, |X|=\lambda\}|$
32325
Can there be a valid argument which has a tautology as a conclusion?
113083
How to prove a set equality?
144396
fitch style proof problem regarding rule of inferences
119888
Is it possible to convert $\forall$ quantifiers to $\exists$ quantifiers without negation?
111122
Proof of a theorem in Hilbert's system
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)
88188
Explain proof by contradiction.
15354
Formal proof of $\exists x \forall y P(x,y) \implies \forall y \exists x P(x,y)$
48213
proving logical equivalence $(P \leftrightarrow Q) \equiv (P \wedge Q) \vee (\neg P \wedge \neg Q)$