مَرَرْتُ بِرَجُلٍ أَفْضَلَ مِنْ خَالِدٍ.
Rajulin is genitive by bi. Afḍala is an agreeing genitive adjective marked with fatḥa because it is diptote; Khālidin is genitive by min.
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A Diptote Genitive Example
Ism al-Tafḍīl: Formation, Comparison, Agreement and Parsing
مَرَرْتُ بِرَجُلٍ أَفْضَلَ مِنْ خَالِدٍ.
Rajulin is genitive by bi. Afḍala is an agreeing genitive adjective marked with fatḥa because it is diptote; Khālidin is genitive by min.