لَمْ يَكْتُبْنَ.
Lam yaktubna is built on sukūn in a jussive position; lam yaktub has actual jussive sukūn on a declinable singular imperfect.
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Lam with Feminine Plural
The Imperfect Verb: Recognition, Time, Prefixes and Mood
لَمْ يَكْتُبْنَ.
Lam yaktubna is built on sukūn in a jussive position; lam yaktub has actual jussive sukūn on a declinable singular imperfect.