Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  d : A
  d' : A
  Γ : list A
  Γ' : list A
  H : All2_fold P Γ Γ'
  p : P Γ Γ' d d'
  IHAll2_fold : ∀ (H := CoreTactics.block) (Γ0 : list A),
                  {| pr1 := Γ0; pr2 := Γ0 |} = {| pr1 := Γ; pr2 := Γ' |}
                  → let H0 := CoreTactics.block in
                    let H1 := CoreTactics.block in
                    All_fold (λ (Γ : list A) (d : A), P Γ Γ d d) Γ0
  ============================
   (∀ Γ0 : list A,
      {| pr1 := Γ0; pr2 := Γ0 |} = {| pr1 := d :: Γ; pr2 := d' :: Γ' |}
      → let H := CoreTactics.block in
        let H0 := CoreTactics.block in
        All_fold (λ (Γ : list A) (d : A), P Γ Γ d d) Γ0)


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.