لَا رَجُلٌ أَفْضَلَ مِنْكَ — lā like laysa: nominative ism + accusative khabar.
لَا رَجُلَ قَائِمٌ — generic lā: ism built on fatḥ in the accusative position + nominative khabar.
لَا تَكْتُبْ — prohibitive lā, which makes the present verb jussive; not an ism–khabar construction.
The third example is only a contrast; the printed passage treats the first two.
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Ism of Mā and Lā Resembling Laysa; Khabar of Lā of Generic Negation
لَا رَجُلٌ أَفْضَلَ مِنْكَ — lā like laysa: nominative ism + accusative khabar.
لَا رَجُلَ قَائِمٌ — generic lā: ism built on fatḥ in the accusative position + nominative khabar.
لَا تَكْتُبْ — prohibitive lā, which makes the present verb jussive; not an ism–khabar construction.
The third example is only a contrast; the printed passage treats the first two.