mathlib3

4481a561 - feat(algebra/group_power/order): Add sq_zero_iff (#13670)

feat(algebra/group_power/order): Add sq_zero_iff (#13670) Tiny lemma that seems to be missing. Should this be a simp lemma? Co-authored-by: Yury G. Kudryashov <urkud@urkud.name>