Proof using.
eauto using sorted_subseq, subseq_skip, subseq_refl.
Qed.

Lemma contiguous_sorted_last :
forall l x i,
sorted (l ++ [x]) ->
contiguous_range_exact_lo (l ++ [x]) i ->
eIndex x = S i /\ contiguous_range_exact_lo l (S i).