Which special vocative feature appears in a-fāṭima?

Imruʾ al-Qays: Address to Fāṭimah, Parting, and the Arrows of the Eyes (Verses 19–22)

• Converting the name into a dual form
• Turning the name into a negative imperative
• Adding a feminine suffix at the start
• Vocative truncation of Fāṭimah to Fāṭim