Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  Γ : list A
  H : All2_fold P Γ Γ
  ============================
   (let H := CoreTactics.block in
    All_fold (λ (Γ : list A) (d : A), P Γ Γ d d) Γ)


DEBUG:Going to execute:
fun tac => lazymatch goal with
                      | H:_ |- _ => tac H
                      end