For a noun, additional alif-nūn combines with proper-name status: ʿImrān and ʿUthmān.
For an adjective, inspect its feminine: sakrān → sakrā; nadmān (companion) → nadmāna.
The book’s marginal note adds that nadmān meaning regretful has feminine nadmā and is a diptote.
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Diptote Causes — Additional Alif and Nūn and Their Conditions
For a noun, additional alif-nūn combines with proper-name status: ʿImrān and ʿUthmān.
For an adjective, inspect its feminine: sakrān → sakrā; nadmān (companion) → nadmāna.
The book’s marginal note adds that nadmān meaning regretful has feminine nadmā and is a diptote.