Goal:
  
  A : Type
  B : Type
  C : Type
  P : nat → A → B → Type
  Q : B → C → Type
  R : B → C → Type
  n : nat
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in
    (∀ (n : nat) (x : A) (y : B) (z : C), P n x y → Q y z → R y z)
    → All2 R [] [])


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 3: T
 has value 
(let H := CoreTactics.block in
 (∀ (n : nat) (x : A) (y : B) (z : C), P n x y → Q y z → R y z)
 → All2 R [] [])