Goal:
  
  A : Type
  R1 : A → A → Type
  R2 : A → Type
  R3 : A → Type
  hd : A
  tl : list A
  tl' : list A
  o : OnOne2 R1 tl tl'
  IHo : All R2 tl
        → (∀ x : A, R2 x → R3 x)
          → (∀ x y : A, R1 x y → R2 x → R3 y) → All R3 tl'
  H1 : list A
  ============================
   (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:
intros p