Goal:
  
  A : Type
  R1 : A → A → Type
  R2 : A → Type
  R3 : A → Type
  hd : A
  hd' : A
  tl : list A
  p : R1 hd hd'
  H1 : list A
  H : All R2 H1
  ============================
   (hd :: tl = H1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      (∀ x : A, R2 x → R3 x)
      → (∀ x y : A, R1 x y → R2 x → R3 y) → All R3 (hd' :: tl))


DEBUG:Going to execute:
fun tac p =>
             let ty := type of p in
             let eliminator := eval simpl in DepElim.elim in
             tac p eliminator