mathlib

216aecd7 - feat(group_theory/quaternion_group): define the (generalised) quaternion groups (#6683)

feat(group_theory/quaternion_group): define the (generalised) quaternion groups (#6683) This PR introduces the generalised quaternion groups and determines the orders of its elements. Co-authored-by: Julian-Kuelshammer <68201724+Julian-Kuelshammer@users.noreply.github.com>