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.</p> Signup and view all the answers

    What is the consequence of the second incompleteness theorem?

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

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