proposition: Lemma eqR_mul2l {r r1 r2} : r <> 0 -> (r * r1 = r * r2) <-> (r1 = r2).
proof: Proof. by move=> r0; split => [/Rmult_eq_reg_l/(_ r0) | ->]. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum) Reals mathcomp(lra) mathcomp(Rstruct)