From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer refutes his father-in-law on several Talmudic questions: he proves that Ulla himself derives ye'ush k'dei lo kani from Scripture and that mitzvah haba'ah ba'aveirah applies universally to all sacrifices; he explains that the rescuer's acquisition in CM 181 operates via hefker rather than standard ye'ush; and he offers original resolutions to difficulties in the Gittin sugyos concerning get delivery and the positions of Shmuel, Rav Huna, and Rabbah.
Source: Shu"t Chasam Sofer CM §155