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 findAtIndex_uniq_equal : forall e e' es, findAtIndex es (eIndex e) = Some e' -> In e es -> uniqueIndices es -> e = e'.