Goal:
  
  hd : A.t
  tl : t
  tl' : t
  X : lt_ tl tl'
  IHX : let H := CoreTactics.block in
        forall x : t,
        {| pr1 := x; pr2 := x |} = {| pr1 := tl; pr2 := tl' |} ->
        let H0 := CoreTactics.block in let H1 := CoreTactics.block in False
  ============================
   (forall x : t,
    {| pr1 := x; pr2 := x |} = {| pr1 := hd :: tl; pr2 := hd :: tl' |} ->
    let H := CoreTactics.block in let H0 := CoreTactics.block in False)


DEBUG:Going to execute:
let H := fresh x in
           intro
           H
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.