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    Gentzen's ordinals are assigned to finite syntactic objec... — Carmelics
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    Challenges→There is an intrinsic connection between Gentzen's ordinal assignment to deductions in PA and the standard ordinal assignment to infinite deductions in PA_ω

    Gentzen's ordinals are assigned to finite syntactic objects while PA_ω ordinals are assigned to infinite trees, making them objects of fundamentally different ontological categories.

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    Key Terms

    Gentzen
    Gerhard Gentzen was a German mathematician and logician (1909-1945) who made groundbreaking contributions to understanding how mathematical proofs work. He's famous for inventing "natural deduction," a system that mirrors how mathematicians actually reason step-by-step, and for developing sequent calculus, a formal framework for studying logic itself. His work laid the foundation for modern logic and computer science, though his career was tragically cut short during World War II.
    Infinite trees(as the type of objects PA_ω ordinals are assigned to)
    Tree-like diagrams in logic that have branches that can go on forever, used to represent logical structures that don't have a finite end point.
    PA_ω(Formal proof theory / ordinal analysis)
    The sequent-style version of Peano arithmetic with the ω-rule; a formal system that discards free variables so that all terms and formulae are closed
    Syntactic(as used in linguistics)
    Related to the rules and structure of how words are arranged in language, rather than their meaning.

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    finite(Bradley's metaphysics)
    An entity that has something that limits it.
    ontological categories(Thomasson's system; used to address mutual exclusiveness and exhaustiveness requirements)
    Classifications of purported entities distinguished by the relations of dependence they have or lack — specifically dependence on mental states and dependence on spatio-temporally located objects.
    ordinals(Proof-theoretic treatment of ordinals, distinct from but related to set-theoretic ordinals)
    A central concept in both set theory and proof theory, used by Gentzen to assign measures to proofs in order to demonstrate consistency of PA via well-foundedness

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    All sources support it1 linkedProof of definition segments1 linked

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    There is an intrinsic connection between Gentzen's ordinal assignment to deducti...

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