Validity of ∃x(Qx→∀x Qx ).
1027
Why is this true? $(\exists x)(P(x) \Rightarrow (\forall y) P(y))$
63656
Ways to write 'P => Q'
45481
Prove or disprove validity: $(\forall x \exists y (P(x) \supset Q(y))) \supset(\exists y \forall x (P (x) \supset Q(y)))$
47222
Soundness of a rule of a proof system with respect to the truth tables?
142762
how to prove that (P⊃Q)≡(¬Q⊃¬P) ( P ⊃ Q ) ≡ ( ¬ Q ⊃ ¬ P ) is disallowed in intuitionistic logic?
86248
Is $\exists x(x=a)$ a valid formula in first order logic with equality?
107967
Significance of assumption in competition inequality questions
79969
Proof that a formula $\theta$ is valid if and only if $\forall x \theta$ is valid
150041
T must be contravariantly valid
72613
FreeQ and arguments of Hypergeometric2F1
108292
Precedence between implication and bi-implication
53056
natural deduction: introduction of universal quantifier and elimination of existential quantifier explained
113605
In Fitch, how does one prove "(P → Q)" from the premise "(¬P ∨ Q)"?
49795
Validity of LTL formulas in a given transition system
67442
Assessing the Quality of a Normal Q-Q Plot
130415
Negating quantifiers with brackets
93544
Nested Quantifiers true or false