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
  ============================
   (#|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:
let ty := type of B in
           intro || (let H := fresh in
                     intro
                     H)
Level 2: Backtrace:

Could not infer a simplification step.
Level 2: Backtrace:

Could not infer a simplification step.
Level 2: Backtrace:

Could not infer a simplification step.
Level 2: Backtrace:

Could not infer a simplification step.