What is the correctly governed form of يَكْتُبُ after lam?

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

• لَمْ يَكْتُبْ
• لَمْ يَكْتُبَ
• لَمْ يَكْتُبُ
• لَمْ يَكْتُبُونَ