Goal:
  
  hd : A.t
  tl'0 : t
  tl : t
  tl' : t
  H : lt_ tl tl'
  IHlt_ : forall z : t, lt tl' z -> lt tl z
  H' : lt_ tl' tl'0
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in lt (hd :: tl) (hd :: tl'0))


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 3: T
 has value 
(let H := CoreTactics.block in lt (hd :: tl) (hd :: tl'0))