What is the main Hanafi–Shafiʿi dispute about qurūʾ?

Legal Implications of Khāṣṣ and the Two Kinds of ʿĀmm

• Hanafi: purity; Shafiʿi: menstruation
• Hanafi: menstruation; Shafiʿi: purity
• Both count days only
• Both reject the number three