proposition: Lemma the_least_pr: has_least r -> least r (the_least r).
proof: Proof. rewrite /the_least=> h; apply: (proj1(select_pr _ _)). by move: h => [z zl];exists z => //; move: zl => [ok _]. by move => x y xsr xlt yset ylt; apply: unique_least. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)