List questions from proof-theory

Published on 14 Jul 2014 - 16:52

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Can we always give a direct proof?

Published on 17 Jul 2014 - 22:20

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Deriving $A \rightarrow ( B \rightarrow C ) \rightarrow ( ( A \rightarrow B ) \rightarrow ( A \rightarrow C ) )$ in the sequent calculus

Published on 30 Jul 2014 - 17:18

333

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What if 'proof by contradiction' is not a valid method of proof?

Published on 26 Mar 2026 - 1:08

256

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Do we know that if $\pi$ is normal then there is a proof of it?

Published on 25 Mar 2026 - 17:40

423

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Is it possible to prove that the encoding of existentials in System F is valid?

Published on 25 Mar 2026 - 19:04

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Is there a way to tell how many different ways you can prove a theorem?

Published on 07 Aug 2014 - 15:34

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What if a conjecture were provably unprovable?

Published on 25 Mar 2026 - 9:36

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The category of theorems and proofs

Published on 19 Aug 2014 - 0:49

443

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Is there a minimal axiomatization of ZFC?

Published on 01 Sep 2014 - 22:28

979

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Problems with nesting proof predicates in first order logic.

Published on 25 Mar 2026 - 12:21

108

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A simple question on Gödel's functional interpretation

Published on 04 Sep 2014 - 3:51

84

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Is a sentence in $\Pi_1$ true given $Q \vdash \lnot\varphi$?

Published on 13 Sep 2014 - 11:36

1k

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What is really a "complete" deductive system for first-order theories.

Published on 25 Mar 2026 - 18:53

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Weakening and Contraction

Published on 16 Sep 2014 - 5:45

List Question

Biconditional statements with an "easy" direction.

Can we always give a direct proof?

Deriving $A \rightarrow ( B \rightarrow C ) \rightarrow ( ( A \rightarrow B ) \rightarrow ( A \rightarrow C ) )$ in the sequent calculus

What if 'proof by contradiction' is not a valid method of proof?

Do we know that if $\pi$ is normal then there is a proof of it?

Is it possible to prove that the encoding of existentials in System F is valid?

Is there a way to tell how many different ways you can prove a theorem?

What if a conjecture were provably unprovable?

The category of theorems and proofs

Is there a minimal axiomatization of ZFC?

Problems with nesting proof predicates in first order logic.

A simple question on Gödel's functional interpretation

Is a sentence in $\Pi_1$ true given $Q \vdash \lnot\varphi$?

What is really a "complete" deductive system for first-order theories.

Weakening and Contraction

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