From: Rabbi Moshe Sofer
To: Rabbi Meir
The Chasam Sofer rules that the chalitzah shoe should have two narrow notches cut in the back, elongated to extend slightly to the sides, rejecting both separate side windows and a single wide notch, in order to expose the yavam's bare skin at the strap's fold-point without rendering the shoe tattered. He also resolves a difficulty in Rabbeinu Yonah by explaining that although epithets like Chanun and Rachum may describe the righteous, they remain valid kinuyim for an oath since one cannot be certain any living person truly possesses these qualities.
Source: Shu"t Chasam Sofer EH II §87