Goal:
  
  A : Type
  a : A
  x : A
  l : list A
  IHl : BinInt.Z.lt BinNums.Z0
          (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH))
        → Some a = nth_error (List.rev l ++ [a]) (#|l| - 0)
  cstr : BinInt.Z.le BinNums.Z0 (BinInt.Z.of_nat #|l|)
  z0 : BinNums.Z
  H0 : BinInt.Z.lt BinNums.Z0
         (BinInt.Z.sub
            (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH))
            BinNums.Z0)
       ∧ z0 =
         BinInt.Z.sub
           (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH))
           BinNums.Z0
       ∨ BinInt.Z.le
           (BinInt.Z.sub
              (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH))
              BinNums.Z0) BinNums.Z0 ∧ z0 = BinNums.Z0
  ============================
   (BinInt.Z.add (BinInt.Z.of_nat #|l|) (BinNums.Zpos BinNums.xH) = z0)


DEBUG:Going to execute:
idtac