إِبْرَاهِيمُ — إِبْرَاهِيمَ — بِإِبْرَاهِيمَ
This is a diptote: no tanwīn, and normally fatḥa in the genitive.
نُوحٌ — نُوحًا — بِنُوحٍ
This is fully declinable by the book’s rule: tanwīn occurs, and the genitive is marked with kasra.
Both are foreign proper names, but the length and middle-letter conditions distinguish them.
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Diptote Causes — Foreign Origin and Its Conditions
إِبْرَاهِيمُ — إِبْرَاهِيمَ — بِإِبْرَاهِيمَ
This is a diptote: no tanwīn, and normally fatḥa in the genitive.
نُوحٌ — نُوحًا — بِنُوحٍ
This is fully declinable by the book’s rule: tanwīn occurs, and the genitive is marked with kasra.
Both are foreign proper names, but the length and middle-letter conditions distinguish them.