Goal:
    hd : A.t  tl : list A.t  H : A.lt hd hd
  ============================
   (let H := CoreTactics.block in let H0 := CoreTactics.block in False)


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 3: T
 has value 
(let H := CoreTactics.block in False)