Goal:
  
  A : Type
  P : list A → A → Type
  Q : list A → list A → A → A → Type
  d : A
  Γ : list A
  d0 : A
  Γ0 : list A
  hlen : #|d :: Γ| = #|d0 :: Γ0|
  ha : All_fold P Γ
  p : P Γ d
  hb : All_fold P Γ0
  ============================
   (P Γ0 d0
    → (∀ (Δ Δ' : list A) (x y : A),
         All_fold P Δ
         → All_fold P Δ' → All2_fold Q Δ Δ' → P Δ x → P Δ' y → Q Δ Δ' x y)
      → (∀ Δ : list A, #|Γ| = #|Δ| → All_fold P Δ → All2_fold Q Γ Δ)
        → let H := CoreTactics.block in All2_fold Q Γ Γ0)


DEBUG:Going to execute:
tac H