proposition: Lemma Qcabs_0 : forall q, Qcabs q = 0 <-> q = 0.
proof: Proof. intros [[[] ?] ?]. reflexivity. reflexivity. unfold Qcabs. simpl. Qcunfold. do 2 rewrite Qceq_Qeq. rewrite Q2Qc_correct. now split; intro H; inversion H. Qed.
imports: Qreduction ClassicalRealizability.Qccomplement