proposition: Lemma amulN x y : `|- x|*|y| == `|x|*|y|.
proof: Proof. by split=> a [b]; do 2?[rewrite absN | exists b]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq order) mathcomp(ssralg ssrnum ssrint rat) fourcolor(real) Coq(Setoid Morphisms)