Goal:
  
  A : Type
  B : Type
  P : list A → list A → A → A → B → Type
  b : B
  a : A
  ls2 : list A
  a0 : A
  ls3 : list A
  X : All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y b) ls2 ls3
  X2 : P ls2 ls3 a a0 b
  ============================
   (All2_fold (λ (l1 l2 : list A) (x y : A), All (P l1 l2 x y) [b]) ls2 ls3)


DEBUG:Going to execute:
solve
[ eauto
| (first [ eapply All2_impl | eapply All2_fold_impl | eapply All_impl ]); tea;
   cbn; intros *; inversion 1 + constructor; subst; eauto ]
Level 0: Backtrace:

In environment
A : Type
B : Type
P : list A → list A → A → A → B → Type
b : B
a : A
ls2 : list A
a0 : A
ls3 : list A
X : All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y b) ls2 ls3
X2 : P ls2 ls3 a a0 b
Unable to unify "All2_fold ?M3112 (?M3113 :: ?M3115) (?M3114 :: ?M3116)" with
 "All2_fold (λ (l1 l2 : list A) (x y : A), All (P l1 l2 x y) [b]) ls2 ls3".
Level 0: Backtrace:

In environment
A : Type
B : Type
P : list A → list A → A → A → B → Type
b : B
a : A
ls2 : list A
a0 : A
ls3 : list A
X : All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y b) ls2 ls3
X2 : P ls2 ls3 a a0 b
Unable to unify "All2_fold ?M3112 (?M3113 :: ?M3115) (?M3114 :: ?M3116)" with
 "All2_fold (λ (l1 l2 : list A) (x y : A), All (P l1 l2 x y) [b]) ls2 ls3".
Level 0: Backtrace:

In environment
A : Type
B : Type
P : list A → list A → A → A → B → Type
b : B
a : A
ls2 : list A
a0 : A
ls3 : list A
X : All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y b) ls2 ls3
X2 : P ls2 ls3 a a0 b
Unable to unify "All2_fold ?M3112 (?M3113 :: ?M3115) (?M3114 :: ?M3116)" with
 "All2_fold (λ (l1 l2 : list A) (x y : A), All (P l1 l2 x y) [b]) ls2 ls3".