Goal:
  
  A : Type
  P : A → A → Type
  Q : A → Type
  HPQ : ∀ x y : A, Q x → P x y → Q y
  hd : A
  hd' : A
  tl : list A
  p : P hd hd'
  H : All Q (hd :: tl)
  ============================
   (All Q (hd' :: tl))


DEBUG:Going to execute:
DepElim.is_introduced H; CoreTactics.block_goal;
            CoreTactics.revert_until H; CoreTactics.block_goal