Why is abī genitive in abī lahab?

Supplementary Practice 23: Comparative Rhetorical Study of Sūrat al-Masad and al-Ikhlāṣ

• It is the subject of tabbat and nominative by yāʾ
• It is an accusative adjective of lahab
• It complements yadā in construct and takes genitive yāʾ as a five-noun form
• It is a vocative after yā and carries tanwīn