List questions from formal-proofs

Published on 23 Feb 2026 - 12:01

84

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$\vdash_L ((B \longrightarrow C)\longrightarrow B) \longrightarrow B$ Using the Deduction Theorem

Published on 06 Apr 2022 - 22:26

245

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Lean and inaccessible cardinals

Published on 24 Mar 2026 - 13:14

78

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How to disprove that $∀_x (p(x)∨q(x))⊨∀_x p(x)∨∀_x q(x)$ with an interpretaion

Published on 23 Apr 2022 - 2:04

251

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A natural deduction proof of $\neg (A \leftrightarrow \neg A ) $.

Published on 25 Apr 2022 - 17:33

82

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Check a proof using structural induction of a formula constructed from a grammar

Published on 26 Apr 2022 - 16:12

83

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Prove that, for any positive real numbers a, b, and c, $a^3b^2 + a^2b^3 + a^3c^2 + a^2c^3 + b^3c^2 + b^2c^3 \geq \frac{a^5 + b^5 + c^5}{5}$.

Published on 27 Apr 2022 - 21:17

53

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Proving a statement to be true using a statement that is sometimes true

Published on 08 May 2022 - 23:53

112

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Summation of squared 3-j symbol

Published on 23 Feb 2026 - 10:17

78

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Consistent, but $ω$-contradictory first-order theory?

Published on 25 May 2022 - 19:11

70

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non-constructive existence of a number

Published on 17 Jun 2022 - 9:34

108

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Natural deduction moving quantifiers

Published on 28 Jun 2022 - 9:34

287

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What does it really mean for a formal system to be consistent?

Published on 26 Mar 2026 - 16:10

72

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What proof system is this paper by Hamano and Okada introducing?

Published on 05 Jul 2022 - 9:37

21

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A fast growing functions in $\sf{ACA_0}$ and $\sf{Z_2}$

Published on 11 Jul 2022 - 20:37

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Is this a valid proof concerning Mersenne Primes?

$\vdash_L ((B \longrightarrow C)\longrightarrow B) \longrightarrow B$ Using the Deduction Theorem

Lean and inaccessible cardinals

How to disprove that $∀_x (p(x)∨q(x))⊨∀_x p(x)∨∀_x q(x)$ with an interpretaion

A natural deduction proof of $\neg (A \leftrightarrow \neg A ) $.

Check a proof using structural induction of a formula constructed from a grammar

Prove that, for any positive real numbers a, b, and c, $a^3b^2 + a^2b^3 + a^3c^2 + a^2c^3 + b^3c^2 + b^2c^3 \geq \frac{a^5 + b^5 + c^5}{5}$.

Proving a statement to be true using a statement that is sometimes true

Summation of squared 3-j symbol

Consistent, but $ω$-contradictory first-order theory?

non-constructive existence of a number

Natural deduction moving quantifiers

What does it really mean for a formal system to be consistent?

What proof system is this paper by Hamano and Okada introducing?

A fast growing functions in $\sf{ACA_0}$ and $\sf{Z_2}$

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