The two forms differ in grammar, not just punctuation: rajulun is nominative under lā like laysa, while rajula is built on fatḥ under generic-negating lā.
Always identify which construction is being used.
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Frequent Mistake: Treating All Lā as the Same
Ism of Mā and Lā Resembling Laysa; Khabar of Lā of Generic Negation
The two forms differ in grammar, not just punctuation: rajulun is nominative under lā like laysa, while rajula is built on fatḥ under generic-negating lā.
Always identify which construction is being used.