proposition: Lemma segment_alt r x a: least r a -> segment r x = interval_co r a x.
proof: Proof. move => [ais lea]; set_extens t; move /Zo_P => [pa pb]; apply/Zo_P;fprops. by move: pb => [_]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)