Kataba is past; uktubanna is imperative. Nūn is licensed by command or request-oriented future context, not all verbs indiscriminately.
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Do Not Add Nūn to a Past Verb
The Two Emphatic Nūns: Forms and Rules
Kataba is past; uktubanna is imperative. Nūn is licensed by command or request-oriented future context, not all verbs indiscriminately.