Goal:
  
  A : Type
  B : Type
  P : A → Type
  Q : A → B → Type
  b : B
  l' : list B
  x : A
  l : list A
  p : P x
  H1 : All P l
  H2 : ∀ (x : A) (y : B), In y (b :: l') → P x → Q x y
  H : #|l| = #|l'|
  ============================
   (let H := CoreTactics.block in
    (∀ l' : list B,
       (∀ (x : A) (y : B), In y l' → P x → Q x y)
       → #|l'| = #|l| → All2 Q l l')
    → let H0 := CoreTactics.block in All2 Q (x :: l) (b :: l'))


DEBUG:Going to execute:
match goal with
           | |- let _ := CoreTactics.block in ?T =>
                 match T with
                 | context [ CoreTactics.block ] =>
                     change T; CoreTactics.intros_until_block
                 end
           | _ => CoreTactics.unblock_goal
           end