-alias symbol "upp" = "uppper".
-alias symbol "leq" = "Ordered set less or equal than".
-lemma cases_in_segment:
- ∀C:half_ordered_set.∀s:segment C.∀x. x ∈ s → seg_l C s (λl.l ≤≤ x) ∧ seg_u C s (λu.x ≤≤ u).
-intros; unfold in H; cases (wloss_prop C) (W W); rewrite<W in H; [cases H; split;assumption]
-cases H; split; assumption;
-qed.
-