Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-adaptedPipeline-generatedjudge pass (gpt-5.6-terra)audited 2026-09-14
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An atom-free symmetric model has countable pairs without choice

Statement

The atom-free socks symmetric extension is a ZF model containing the countable family (Pn) of pairs of sets of reals but no choice function; ACω,2 fails directly in pure ZF.

Facts & Assumptions

Given: The hypotheses, objects, and conventions in the Statement.

[F1]

The atom-free socks symmetric system gives the pair sequence and coordinate group.

[F2]

Symmetry lemma for forcing automorphisms transports a choice decision under a swap.

[F3]

Choice for pairs and countable finite choice identifies the failed principle.

Proof

1.1

F1 makes every Pn and the indexed sequence HS, so the symmetric ZF model regards its range as countable pairs. Distinct-coordinate dense sets ensure Rn,0Rn,1.

F1
1.2

Suppose pc˙(n)P˙n for a supported choice name c˙. Choose n outside the finitely many supported pair indices and strengthen to qp deciding, say, c˙(n)=R˙n,0. Choose a block swap at n that fixes the support. By additionally permuting unused j-coordinates in that block, arrange that q and its image have disjoint moved domains and hence are compatible.

F1
2.1

F2 says the image condition forces the same c˙(n) to equal R˙n,1. A common extension then forces the two distinct mates equal, contradiction. Therefore no choice function exists and F3 fails. The construction is in pure ZF and uses neither the Recorded transfer result nor AC.

F2F3step 1.2

Depends on

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Sources