The condensed Whitehead conjecture for complete Boolean algebras

Let AA be an abelian group and let B\mathbb{B} be a complete Boolean algebra. Write S(B)S(\mathbb{B}) for the associated Stone space, and let BA\Vdash_{\mathbb{B}} “A is not Whitehead"" mean that B\mathbb{B} forces that AA is not a Whitehead group. Let A\underline{A} and Z\underline{\mathbb{Z}} denote the corresponding condensed abelian groups, and let ExtCondAb1\underline{\mathrm{Ext}}^1_{\mathsf{CondAb}} denote the condensed Ext functor.

The condensed Whitehead conjecture. Suppose that AA is an abelian group, B\mathbb{B} is a complete Boolean algebra, and

BA is not Whitehead".\Vdash_{\mathbb{B}} “A \text{ is not Whitehead}".

Then

ExtCondAb1(A,Z)(S(B))0.\underline{\mathrm{Ext}}^1_{\mathsf{CondAb}}(\underline{A},\underline{\mathbb{Z}})(S(\mathbb{B}))\neq 0.

The conjecture proposes that the technical strengthening of the failure of AA to be Whitehead used in the paper's theorem is unnecessary. It is refuted: the converse does not hold, as shown in the discussion following Corollary.

Sources & referencesView supporting material

Primary source

Jeffrey Bergfalk, Chris Lambie-Hanson and Jan Šaroch, “Whitehead's problem and condensed mathematics”, arXiv:2312.09122 (2025).

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