Theorem Subgroup.relIndex_eq_two_iff_exists_notMem_and'

Modification history

2025-10-22 18:34
Mathlib/GroupTheory/Index.lean
feat(GroupTheory/Index): criteria for subgroup to have index 2 (#30466) …
Added Subgroup.relIndex_eq_two_iff_exists_notMem_and'View on Github →