Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  Q : list A → A → Type
  d : A
  d' : A
  Γ : list A
  Γ' : list A
  X : All2_fold P Γ Γ'
  p : P Γ Γ' d d'
  IHX : All_fold Q Γ
        → All_fold Q Γ'
          → All2_fold
              (λ (Γ Γ' : list A) (x y : A), Q Γ x × Q Γ' y × P Γ Γ' x y) Γ Γ'
  l : All_fold Q (d :: Γ)
  r : All_fold Q (d' :: Γ')
  ============================
   (All2_fold (λ (Γ Γ' : list A) (x y : A), Q Γ x × Q Γ' y × P Γ Γ' x y)
      (d :: Γ) (d' :: Γ'))


DEBUG:Going to execute:
DepElim.do_intros H; DepElim.generalize_by_eqs H
Level 1: evaluation returns
DepElim.do_intros H; DepElim.generalize_by_eqs H; tac H
where
tac := fun hyp => DepElim.do_case hyp
       where
       id := l
       of type
       constr
of type
tacvalue
H := l
of type
constr of type tacvalue