Which form belongs to this lesson's emphatic construction rather than the separate particle لَنْ?

Emphasis in the Imperfect: Light and Heavy Nun

• لَنْ يَفْعَلَ
• لَا يَفْعَلُ
• سَوْفَ يَفْعَلُ
• لَيَفْعَلَنَّ