Why " provided $t$ is not in $\theta$ " at the end of the definition of $\forall $ Intro Rule ? ( Shapiro's Entry On Classical Logic in SEP)
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natural deduction: introduction of universal quantifier and elimination of existential quantifier explained
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Cancellation Law for Direct Sums - What is wrong with this argument?
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Validity of LTL formulas in a given transition system
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In classical logic, why is $(p\Rightarrow q)$ True if $p$ is False and $q$ is True?
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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
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Time complexity function in terms of theta notation
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Why is this true? $(\exists x)(P(x) \Rightarrow (\forall y) P(y))$
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Ambiguity of notation: $\sin(x)^2$
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Choice of $q$ in Baby Rudin's Example 1.1
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The negation of a limit condition, Spivak style.
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Proof Verification: Converse of Intermediate Value Theorem
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Trying to prove $p,p \to (r \to q) \vdash (\neg q \to \neg r)$ by using natural deduction.
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What came first, the $\forall$ or the $\exists$?
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fitch style proof problem regarding rule of inferences
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Proof, is $\forall x : (P(x) \lor Q(x)) \Leftrightarrow \forall x : P(x) \lor \forall x : Q(x)$?
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In Fitch, how does one prove "(P → Q)" from the premise "(¬P ∨ Q)"?
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Why do I have to solve for $x$ in this proof, if I choose not to find a counterexample?