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 Γ
  q : Q Γ d
  r1 : list A
  r : All_fold Q r1
  ============================
   (d' :: Γ' = r1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      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:
try rename id into id',id' into id
Level 3: evaluation returns
try rename id into id',id' into id; cont id'1 id
where
t := d' :: Γ'
of type
constr
id'1 := r1
of type
constr
id' := r
of type
intropattern
id := r
of type
intropattern
cont := fun id id' => DepElim.decompose_exists id id'
        where
        id := r
        of type
        intropattern
of type
tacvalue of type tacvalue