What is the correctly governed form of يَكْتُبُ after lan?

Negating the Imperfect with Lan and Lam: Subjunctive, Jussive and Full Paradigms

• لَنْ يَكْتُبُ
• لَنْ يَكْتُبْ
• لَنْ يَكْتُبَ
• لَنْ يَكْتُبُونَ