proposition: Lemma pl_neg_l@{} x : equiv (- x + x) 0.
proof: Proof. red;simpl. rewrite mult_1_r, mult_0_l. rewrite <-plus_mult_distr_r. rewrite plus_negate_l. apply mult_0_l. Qed.
imports: HoTT.HIT.quotient HoTT.Basics.Trunc HoTT.Classes.interfaces.abstract_algebra HoTT.Classes.theory.dec_fields