Is $A \to \neg A$ logically satisfiable if $A$ is false?
130080
How is the statement $\bot \to \top$ true?
113344
How do we prove that something is unprovable?
105303
'Obvious' theorems that are actually false
6166
Is the following statement provable?
45481
Prove or disprove validity: $(\forall x \exists y (P(x) \supset Q(y))) \supset(\exists y \forall x (P (x) \supset Q(y)))$
103112
Does the existential quantifier distribute over an implication?
21035
Clarifying on how if p,q is logically equivalent to p only if q
41622
Converting truth tables to boolean expressions
142762
how to prove that (P⊃Q)≡(¬Q⊃¬P) ( P ⊃ Q ) ≡ ( ¬ Q ⊃ ¬ P ) is disallowed in intuitionistic logic?
140194
Using natural deduction to prove that $p \implies q \vdash \lnot p \lor q$
13074
Prove Logical Equivalence
32929
Questions about proving $\lnot \lnot a = a$
48213
proving logical equivalence $(P \leftrightarrow Q) \equiv (P \wedge Q) \vee (\neg P \wedge \neg Q)$
42590
Understanding implication in logic truth tables (excerpt from textbook)
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
121361
Showing that $\lnot Q \lor (\lnot Q \land R) = \lnot Q$ without a truth table
82739
Why is $\alpha \rightarrow \forall x(\alpha)$ not generally correct in first-order logic?