Modified Onshuus–Pillay conjecture with a small-model-definable subgroup

Let MM be a highly saturated PP-minimal structure over a pp-adic field KK, let GG be a definable group, and set n=dim(G)n=\dim(G). Let M0MM_0\prec M be a small model defining GG. Recall that G00G^{00} is the smallest type-definable subgroup of GG of small index, and that HH is compactly dominated by H/H00H/H^{00} when the quotient map satisfies the compact-domination condition with respect to normalized Haar measure. Modified Onshuus–Pillay conjecture. There is an nn-dimensional M0M_0-definable open subgroup HGH\subseteq G such that

H/H00H/H^{00}

is isomorphic to an nn-dimensional Lie group over KK, and HH is compactly dominated by H/H00H/H^{00}. This strengthens the original formulation by requiring the subgroup to be definable over the fixed small model M0M_0. The source says that the original Onshuus–Pillay conjecture is technically resolved, but that the author does not know how to prove this modified variant; it is therefore open.

Sources & referencesView supporting material

Primary source

Will Johnson, “Generic differentiability and P-minimal groups”, arXiv:2404.17234 (2026).

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