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#settheory — Public Fediverse posts

Live and recent posts from across the Fediverse tagged #settheory, aggregated by home.social.

  1. Late to the party, but I heart “Rethinking Set Theory”, Tom Leinster’s presentation of ETCS (arxiv.org/abs/1212.6543). My natal foundation is higher-order logic, and this is the first time set theory has made any sense to me, other than as a technical device.

    Bonus lecture notes: webhomes.maths.ed.ac.uk/~tl/as

    #settheory #etcs #higherorderlogic

  2. So we have { 1, 2 } ∈ Fin₁ ⊆ Fin₁ₐ ⊆ Fin₂ ⊆ Fin₃ ⊆ Fin₄ ⊆ Fin₅ ⊆ Fin₆ ⊆ Fin₇

    If a set is in Fin₁ then it is considered finite by all the other definitions.

    But since the axiom of choice is equivalent to saying every set can be well-ordered, if we accept it VII-finite sets are equinumerous with a finite ordinal and so Fin₇ ⊆ Fin₁ and so the differences between these definitions collapse and ZF becomes ZFC, which is a widely accepted basis for Set Theory.

    My consultation with math resources was inspired by a blog post:

    infinitelymore.xyz/p/what-is-t

    #Metamath #ZFC #SetTheory #AxiomOfChoice #FiniteSet #Infinity

  3. Any #mathematics professors want to take a shot at explaining to someone with say a typical math major undergrad background what the deal is with the recent introduction of exacting and ultraexacting cardinals?

    #math #maths #settheory #zfc

    arxiv.org/abs/2411.11568

  4. Interesting read about #mathematics, #settheory, and #informationtheory from Quanta Magazine, about getting closer to resolving the union-closed conjecture. It references the 1948 paper, “A Mathematical Theory of Communication" from #claudeshannon.

    quantamagazine.org/long-out-of