Definition contiguous_range_exact_lo xs lo :=
    (forall i,
       lo < i <= maxIndex xs ->
       exists e,
         eIndex e = i /\
         In e xs) /\
    (forall e,
       In e xs ->
       lo < eIndex e).

Lemma findGtIndex_necessary : forall entries e x, In e (findGtIndex entries x) -> In e entries /\ eIndex e > x.