Gödel's Incompleteness Theorem and Gentzen's Proof
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Questions and Answers

What is the significance of Gentzen's theory in relation to first-order Peano arithmetic (PA)?

  • Gentzen's theory is stronger than PA.
  • Gentzen's theory is a subtheory of PA.
  • Gentzen's theory is a weaker theory than PA.
  • Gentzen's theory is incomparable to PA. (correct)

What can be proved in Gentzen's theory that cannot be proved in PA?

  • The consistency of PA. (correct)
  • Ordinary mathematical induction for all formulae.
  • The completeness of PA.
  • The inconsistency of PA.

What is the significance of the notion of interpretability?

  • It is used to prove the inconsistency of a theory.
  • It is used to show the completeness of a theory.
  • It is used to compare the strength of two theories. (correct)
  • It is used to prove the consistency of a theory.

What can be conclude about theory T if it is interpretable in another theory B?

<p>T is consistent if B is consistent. (D)</p> Signup and view all the answers

What is the consequence of the second incompleteness theorem?

<p>A theory cannot prove its own consistency. (C)</p> Signup and view all the answers

What is the relationship between the consistency of theory T and theory B if T is interpretable in B?

<p>T is consistent if B is consistent. (B)</p> Signup and view all the answers

What is the idea that motivates the use of interpretability to compare theories?

<p>That, if B interprets T, then B is at least as strong as T (B)</p> Signup and view all the answers

What does Pudlák's result state about a consistent theory T that contains Robinson arithmetic, Q?

<p>T cannot interpret Q plus Con(T) (D)</p> Signup and view all the answers

What is true about Q+Con(T) and T, according to the arithmetized completeness theorem?

<p>Q+Con(T) is stronger than T (A)</p> Signup and view all the answers

Why can't PA interpret Gentzen's theory, according to Pudlák's result?

<p>Because Gentzen's theory interprets Q+Con(PA) and interpretability is transitive (A)</p> Signup and view all the answers

What is true about Gentzen's theory and PA, in terms of consistency strength?

<p>Gentzen's theory is stronger than PA (C)</p> Signup and view all the answers

What is required for a theory to be stronger than another theory, in terms of consistency strength?

<p>That the stronger theory interprets the weaker theory (A)</p> Signup and view all the answers

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