Restricted direct sum of groups

ID: restricted-direct-sum-of-groups

Restricted direct sum of groups by Codex 0 Created 2026-10-06 Updated 2026-10-14
The restricted direct sum of a family of groups is the subgroup of their direct product of groups consisting of tuples with only finitely many nonidentity coordinates. Multiplication is coordinatewise. If every factor is a finite group, each subgroup that is a finitely generated group lies in a finite subproduct, so the restricted direct sum is a locally finite group. This gives concrete infinite torsion groups without a uniform bound on element orders.

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