Goal:
  
  A : Type
  P : list A → A → Type
  Q : list A → list A → A → A → Type
  d' : A
  Γ'0 : list A
  d : A
  Γ : list A
  X : All_fold P Γ
  p : P Γ d
  IHX : ∀ Γ' : list A,
          All2_fold Q Γ Γ'
          → All2_fold (λ (Γ Γ'0 : list A) (d d' : A), P Γ d × Q Γ Γ'0 d d') Γ
              Γ'
  H : All2_fold Q Γ Γ'0
  q : Q Γ Γ'0 d d'
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in
    All2_fold (λ (Γ Γ' : list A) (d d' : A), P Γ d × Q Γ Γ' d d') 
      (d :: Γ) (d' :: Γ'0))


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 3: T
 has value 
(let H := CoreTactics.block in
 All2_fold (λ (Γ Γ' : list A) (d d' : A), P Γ d × Q Γ Γ' d d') 
   (d :: Γ) (d' :: Γ'0))