refine Commute.of_orderOf_dvd_two (fun g => ?_) a b
G : Type u_1
inst✝ : Group G
h : ∀ (g : G), g = 1 ∨ orderOf g = 2
a b : G
⊢ a * b = b * a
G : Type u_1
inst✝ : Group G
h : ∀ (g : G), g = 1 ∨ orderOf g = 2
a b g : G
⊢ orderOf g ∣ 2