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set theory – ULTRAVALIDITY

ULTRAVALIDITY

Tag: set theory

  • When do two injections make a bijection?

    On some proofs of the Schroeder-Bernstein theorem. A version of this article originally appeared in The Oxford Invariants Society magazine The Invariant in Trinity Term 2015. 1. Motivation: Sets, sizes and injections How do we know whether two sets are the same size, in other words, that they have the same number of elements? For small, finite…