Corollary Forall_sublist_first : forall {A} {d : Inhabitant A} (P : A -> Prop) i j l
  (Hrangei : 0 <= i <= Zlength l) (Hi : Forall P (sublist 0 i l)) (Hi' : ~P (Znth i l))
  (Hrangej : 0 <= j <= Zlength l) (Hj : Forall P (sublist 0 j l)) (Hj' : ~P (Znth j l)),
  i = j.

Lemma signed_inj : forall i1 i2, Int.signed i1 = Int.signed i2 -> i1 = i2.