978. An appositive in the genitive may follow an adjective equivalent to a genitive: Ἀθηναῖος ( = Ἀθηνῶν) ὤν, πόλεως τῆς μεγίστης being an Athenian, a citizen of the greatest city P. A. 29d.
Why doesn't he say "(=Ἀθηναῖοu)", singular genitive? ὤν is singular. πόλεως is singular genitive. What am I missing?
Thanks in advance.