Goal:
  
  A : Type
  i : nat
  IHi : ∀ l : list A,
          i < #|l| → nth_error l i = nth_error (List.rev l) (#|l| - S i)
  a : A
  l : list A
  H : BinInt.Z.lt
        (BinInt.Z.add (BinInt.Z.of_nat i) (BinNums.Zpos BinNums.xH))
        (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH))
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat i)
  cstr0 : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat #|l|)
  ============================
   (BinInt.Z.lt (BinInt.Z.of_nat i) (BinInt.Z.of_nat #|l|))


DEBUG:Going to execute:
idtac