From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer permits a yavam to marry another woman when the yevamah refuses to travel for chalitzah, classifying her as a moredet, provided beis din first warns her and the yavam swears to perform chalitzah promptly upon her appearance. He resolves the conflict between the Maharik and Hagahos Maimuniyos by distinguishing different factual scenarios, and validates a post-zikah oath to perform chalitzah by distinguishing it from an impermissible pre-zikah oath.
Source: Shu"t Chasam Sofer EH II §80