Goal:
  
  A : Type
  P : list A → A → Type
  Q : list A → list A → A → A → Type
  d : A
  Γ : list A
  hlen : #|d :: Γ| = #|[]|
  ha : All_fold P Γ
  p : P Γ d
  ============================
   (let H := CoreTactics.block in
    (∀ (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 H0 := CoreTactics.block in All2_fold Q (d :: Γ) [])


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 3: T
 has value 
((∀ (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 (d :: Γ) [])