Goal:
  
  A : Type
  B : Type
  C : Type
  P : A → B → C → Type
  a : C
  ls1 : list C
  a0 : A
  ls2 : list A
  b : B
  ls3 : list B
  X1 : All2 (λ (x : A) (y : B), All (P x y) (a :: ls1)) ls2 ls3
  X : P a0 b a
  X2 : All (P a0 b) ls1
  ============================
   (All2 (λ (x : A) (y : B), All (P x y) ls1) 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
C : Type
P : A → B → C → Type
a : C
ls1 : list C
a0 : A
ls2 : list A
b : B
ls3 : list B
X1 : All2 (λ (x : A) (y : B), All (P x y) (a :: ls1)) ls2 ls3
X : P a0 b a
X2 : All (P a0 b) ls1
Unable to unify "All2 ?M3378 (?M3379 :: ?M3381) (?M3380 :: ?M3382)" with
 "All2 (λ (x : A) (y : B), All (P x y) ls1) ls2 ls3".
Level 0: Backtrace:

In environment
A : Type
B : Type
C : Type
P : A → B → C → Type
a : C
ls1 : list C
a0 : A
ls2 : list A
b : B
ls3 : list B
X1 : All2 (λ (x : A) (y : B), All (P x y) (a :: ls1)) ls2 ls3
X : P a0 b a
X2 : All (P a0 b) ls1
Unable to unify "All2 ?M3378 (?M3379 :: ?M3381) (?M3380 :: ?M3382)" with
 "All2 (λ (x : A) (y : B), All (P x y) ls1) ls2 ls3".
Level 0: Backtrace:

In environment
A : Type
B : Type
C : Type
P : A → B → C → Type
a : C
ls1 : list C
a0 : A
ls2 : list A
b : B
ls3 : list B
X1 : All2 (λ (x : A) (y : B), All (P x y) (a :: ls1)) ls2 ls3
X : P a0 b a
X2 : All (P a0 b) ls1
Unable to unify "All2 ?M3378 (?M3379 :: ?M3381) (?M3380 :: ?M3382)" with
 "All2 (λ (x : A) (y : B), All (P x y) ls1) ls2 ls3".