Goal:
  
  A : Type
  B : Type
  P : A → B → Prop
  Q : A → B → Prop
  x : A
  y : B
  l : list A
  l' : list B
  H : P x y
  H0 : Forall2 P l l'
  IHForall2 : Forall (λ x : A, ∀ y : B, P x y → Q x y) l → Forall2 Q l l'
  H1 : Forall (λ x : A, ∀ y : B, P x y → Q x y) (x :: l)
  x0 : A
  l0 : list A
  H4 : ∀ y : B, P x y → Q x y
  H5 : Forall (λ x : A, ∀ y : B, P x y → Q x y) l
  H2 : x0 = x
  H3 : l0 = l
  ============================
   (Forall2 Q l l')


DEBUG:Going to execute:
match reverse goal with
           | id:?X1
             |- _ =>
                 <Coq.Init.Tauto.is_conj> flags X1; elim id; do 2 intro;
                  clear id
           | id:_ ↔ _ |- _ => elim id; do 2 intro; clear id
           | id:¬ _ |- _ => red in id
           | id:?X1
             |- _ =>
                 <Coq.Init.Tauto.is_disj> flags X1; elim id; intro; clear id
           | _ =>
               <Coq.Init.Tauto.find_cut>
                ltac:(fun id0 id1 X2 =>
                        assert X2; [ exact (id0 id1) | clear id0 ])
           | id:?X1 → ?X2
             |- _ =>
                 <Coq.Init.Tauto.is_unit_or_eq> flags X1; Ltac.cut X2;
                  [ intro; clear id
                  | Ltac.cut X1; [ exact id | constructor 1; fail ] ]
           | id:?X1 → ?X2
             |- _ =>
                 <Coq.Init.Tauto.flatten_contravariant_conj> flags X1 X2 id
           | id:?X1 ↔ ?X2 → ?X3
             |- _ =>
                 assert ((X1 → X2) → (X2 → X1) → X3) by
                  (do 2 intro; apply id; Ltac.split; Ltac.assumption); clear
                  id
           | id:?X1 → ?X2
             |- _ =>
                 <Coq.Init.Tauto.flatten_contravariant_disj> flags X1 X2 id
           | |- ?X1 => <Coq.Init.Tauto.is_conj> flags X1; Ltac.split
           | |- _ ↔ _ => Ltac.split
           | |- ¬ _ => red
           end; <Coq.Init.Tauto.not_dep_intros>
Level 2: evaluation returns
<coq-core.plugins.tauto::is_conj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := Q x y
of type
constr of type tacvalue

Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.
Level 0: Backtrace:

No matching clauses for match.
Level 0: Backtrace:

No matching clauses for match.