Goal:
  
  A : Type
  f : nat → A
  n : nat
  i : nat
  hf : ∀ i j : nat, f i = f j → i = j
  H : In (f i) (unfold n f)
  IHn : BinInt.Z.lt (BinInt.Z.of_nat i) (BinInt.Z.of_nat n)
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat i)
  cstr0 : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat n)
  ============================
   (BinInt.Z.lt (BinInt.Z.of_nat i)
      (BinInt.Z.add (BinInt.Z.of_nat n) (BinNums.Zpos BinNums.xH)))


DEBUG:Going to execute:
idtac