Goal:
  
  A : Type
  B : Type
  P : A → B → Type
  Q : A → B → Type
  l' : list B
  X : All2 P [] l'
  X0 : ∀ (x : A) (y : B), In x [] → In y l' → P x y → Q x y
  H0 : [] = l'
  ============================
   (All2 Q [] [])


DEBUG:Going to execute:
<coq-core.plugins.ltac::econstructor@0>