proposition: Lemma BRabs_opp x: realp x -> BRabs (BRopp x) = BRabs x.
proof: Proof. case/BR_i1P => h. + by rewrite h BRopp_0. + by rewrite (BRabs_negs (BRopp_positive1 h)) (BRopp_K (BRps_sBR h))BRabs_poss. + by rewrite (BRabs_poss (BRopp_negative1 h)) (BRabs_negs h). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)