English
Groups with nilpotency class at most 1 are abelian; conversely, abelian groups have nilpotency class at most 1.
Русский
Группы с классом нильпотентности не более 1 абелевы; наоборот, абелевы имеют такой же предел.
LaTeX
$$$\\operatorname{nilpotencyClass}(G) \\le 1 \\iff \\text{Abelian}(G)$$$
Lean4
/-- Groups with nilpotency class at most one are abelian -/
def commGroupOfNilpotencyClass [IsNilpotent G] (h : Group.nilpotencyClass G ≤ 1) : CommGroup G :=
Group.commGroupOfCenterEqTop <| by
rw [← upperCentralSeries_one]
exact upperCentralSeries_eq_top_iff_nilpotencyClass_le.mpr h