What grammatical effect does “lam” have in “lam yatakhaddad”?

Ṭarafah ibn al-ʿAbd: Ruins, Ships, Gazelle, and Beauty (Verses 1–10)

• it makes the imperfect jussive and negates a past event
• it turns the verb into an imperative
• it makes a subjunctive future assertion
• it governs a genitive noun