proposition: Lemma invR_neq0 x : x != 0 -> x^-1 != 0.
proof: Proof. by move=> nz_x vx0; case: neqR10; rewrite -(divRR nz_x) vx0 mulR0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)