Goal:
  
  A : Type
  l3 : list A
  R1 : A → A → Type
  R2 : A → A → Type
  R3 : A → A → Type
  hd : A
  hd' : A
  tl : list A
  p : R1 hd hd'
  H : All2 R2 (hd :: tl) l3
  ============================
   ((∀ x y : A, R2 x y → R3 x y)
    → (∀ x y z : A, R1 x y → R2 x z → R3 y z) → All2 R3 (hd' :: tl) l3)


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