List questions from formal-proofs

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Find a proof for the following tautology

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Complement function: how to prove surjective?

Published on 18 Sep 2018 - 19:24

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$(P → Q) \lor (Q → R)$, Fitch-style proof

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Prove $\Sigma \vdash \lnot(\phi \rightarrow \psi)$ iff $\Sigma \vdash \phi$ and $\Sigma \vdash \lnot \psi.$

Published on 23 Feb 2026 - 1:21

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Good list of theorems tobprove

Published on 23 Sep 2018 - 2:56

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Book Recommendation

Published on 29 Sep 2018 - 19:23

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How to formalize my intution of this theorem on continuous functions?

Published on 01 Oct 2018 - 13:56

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Let $a,b,c,d$ be real numbers such that $a<b < c<d$. Express the set $[a,b] \cup [c,d]$ as the difference of two sets

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Semantic proofs to syntactic proofs

Published on 03 Oct 2018 - 20:23

272

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Prove $\forall n \in \mathbb N, \forall k\in \mathbb Z, \forall \ell \in \mathbb Z, \neg (n = 5k+3 \land n = 5\ell +1)$, Intended meaning?

Published on 07 Oct 2018 - 5:28

38

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How can I prove this in a systematic manner?

Published on 07 Oct 2018 - 9:50

66

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Prove that a sequence which converges at L, still converges at L when a fixed positive integer is added to the variable.

Published on 08 Oct 2018 - 18:08

243

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Weakest theory equi-consistent to ZFC

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55

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Can a sequent be valid if the conclusion contains atoms that are not in the premise?

Published on 17 Oct 2018 - 9:20

List Question

Formal Proof of WFF using Rules of Inference

Find a proof for the following tautology

Complement function: how to prove surjective?

$(P → Q) \lor (Q → R)$, Fitch-style proof

Prove $\Sigma \vdash \lnot(\phi \rightarrow \psi)$ iff $\Sigma \vdash \phi$ and $\Sigma \vdash \lnot \psi.$

Good list of theorems tobprove

Book Recommendation

How to formalize my intution of this theorem on continuous functions?

Let $a,b,c,d$ be real numbers such that $a<b < c<d$. Express the set $[a,b] \cup [c,d]$ as the difference of two sets

Semantic proofs to syntactic proofs

Prove $\forall n \in \mathbb N, \forall k\in \mathbb Z, \forall \ell \in \mathbb Z, \neg (n = 5k+3 \land n = 5\ell +1)$, Intended meaning?

How can I prove this in a systematic manner?

Prove that a sequence which converges at L, still converges at L when a fixed positive integer is added to the variable.

Weakest theory equi-consistent to ZFC

Can a sequent be valid if the conclusion contains atoms that are not in the premise?

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