The generic bicyclic-unit free-group conjecture

From papers

Let GG be a finite group that is not Dedekind, let RR be the coefficient ring, and let BicR(G)\operatorname{Bic}_R(G) be the group generated by all bicyclic units of RGRG. Fix a bicyclic unit β\beta. The generic bicyclic-unit free-group conjecture. The set

{αBicR(G)α,βαβ canonically}\left\{\alpha\in\operatorname{Bic}_R(G)\mid \langle\alpha,\beta\rangle\cong\langle\alpha\rangle\ast\langle\beta\rangle\ \text{canonically}\right\}

is “large” in BicR(G)\operatorname{Bic}_R(G). The conjecture makes precise the expectation that two bicyclic units generically generate a free product, but the source leaves “large” unspecified; its precise formulation and general validity remain open.

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Sources & referencesView supporting material

Primary source

Geoffrey Janssens, Doryan Temmerman and François Thilmany, “Simultaneous ping-pong for finite subgroups of reductive groups”, arXiv:2510.23957 (2025).

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