proposition: Lemma oprod_Meq1lt b c: \1o <o b -> \0o <o c -> c <o (c *o b).
proof: Proof. move => lt1b cz. rewrite - {1} (oprod1r (proj32_1 cz)); apply: (oprod_Meqlt lt1b cz). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)