Module OrderedTypeLists (O:OrderedType).
Local Notation In:=(InA O.eq).
Local Notation Inf:=(lelistA O.lt).
Local Notation Sort:=(sort O.lt).
Local Notation NoDup:=(NoDupA O.eq).
Notation Sort := (sort ltk).
Notation Inf := (lelistA ltk).

Lemma Sort_In_cons_2 l p q : Sort (p::l) -> InA eqk q (p::l) ->
ltk p q \/ eqk p q.