proposition: Lemma seg_order_wosr r x: worder r -> worder_on (seg_order r x) (segment r x).
proof: Proof. move => wor;split; first exact:(seg_order_wor x wor). exact: (proj2 (seg_order_osr x (proj1 wor))). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)