Posted by Jason Polak on 15. October 2011 · 1 comment · Categories: model-theory, set-theory · Tags: , ,

Here I explain the proof that in ZF, the axiom of choice (AC) is equivalent to every nonempty set having group structure (GS). I first learned of the nontrivial direction of this argument in this MathOverflow post and as far as I know first appeared in "Some new algebraic equivalents of the axiom of choice" by A. Hajnal and A. Kertész in Publ. Math. Debrecen 19 (1972), pp. 339-340.

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