Goal:
    hd : A.t  tl : t  X : lt_ tl tl  IHX : False
  ============================
   (let H := CoreTactics.block in False)


DEBUG:Going to execute:
match goal with
           | |- let _ := CoreTactics.block in _ => intros _
           | |- _ => try (intro; CoreTactics.intros_until_block)
           end