Date: 8 Kislev 5594
From: Rabbi Moshe Sofer
To: Unknown recipient
When a mourning Kohen is the only Kohen present on Shabbos, the Chasam Sofer rules he should be called to the Torah and should not leave the synagogue, since leaving would itself constitute public mourning forbidden on Shabbos. He reconciles the apparent contradiction between SA YD 384 (weekday prohibition) and SA YD 400 (Shabbos leniency) by reinterpreting the Ri"tz Gi'os as addressing only weekday minyanim at the mourner's home, thereby rendering the Maharam's recommendation to leave unnecessary.
Source: Shu"t Chasam Sofer YD §352