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|)
  z1 : BinNums.Z
  H1 : BinInt.Z.lt BinNums.Z0
         (BinInt.Z.sub (BinInt.Z.of_nat #|l|)
            (BinInt.Z.add (BinInt.Z.of_nat i) (BinNums.Zpos BinNums.xH)))
       ∧ z1 =
         BinInt.Z.sub (BinInt.Z.of_nat #|l|)
           (BinInt.Z.add (BinInt.Z.of_nat i) (BinNums.Zpos BinNums.xH))
       ∨ BinInt.Z.le
           (BinInt.Z.sub (BinInt.Z.of_nat #|l|)
              (BinInt.Z.add (BinInt.Z.of_nat i) (BinNums.Zpos BinNums.xH)))
           BinNums.Z0 ∧ z1 = BinNums.Z0
  ============================
   (BinInt.Z.lt z1 (BinInt.Z.of_nat #|l|))


DEBUG:Going to execute:
xlia zchecker