What is the function of fāʾ in “أَمَّا زَيْدٌ فَحَاضِرٌ”?

Aḍrub al-Khabar: Ibtidāʾī, Ṭalabī and Inkārī Reports

• It turns the clause into a question
• It is the noun of inna
• It introduces the response to conditional ammā
• It marks an oath