Goal:
  
  A : Type
  B : Type
  P : B → A → A → Type
  Q : A → Type
  hd : A
  tl : list A
  b : B
  bs : list B
  tl' : list A
  X : OnOne2All P bs tl tl'
  X0 : Q hd
  X1 : All Q tl
  X2 : OnOne2All (λ (i : B) (x y : A), P i x y × Q x) bs tl tl'
  ============================
   (OnOne2All (λ (i : B) (x y : A), P i x y × Q x) bs tl tl')


DEBUG:Going to execute:
match goal with
           | |- ?X1 → ?X2 => intro
           | |- ¬ _ => unfold not at 1; intro
           end