lemma div1: ∀G:dgroup.∀x:G.x/O ≈ x.
intro G; cases G; unfold divide; intros; simplify;
cases (f x O); simplify; simplify in H; intro; apply H;
lemma div1: ∀G:dgroup.∀x:G.x/O ≈ x.
intro G; cases G; unfold divide; intros; simplify;
cases (f x O); simplify; simplify in H; intro; apply H;