Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  d : A
  Γ : list A
  H : All2_fold P Γ Γ
  p : P Γ Γ d d
  IHAll2_fold : All_fold (λ (Γ : list A) (d : A), P Γ Γ d 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) (d :: Γ))


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 3: T
 has value 
(let H := CoreTactics.block in
 All_fold (λ (Γ : list A) (d : A), P Γ Γ d d) (d :: Γ))