Date: 2 Av 5563
From: Rabbi Moshe Sofer
To: Rabbi Itzik Frenkel
The responsum discusses Rambam's ruling that it is forbidden to eat chametz itself, even a small amount, and explores the concept of 'chatzi shiur' (half a measure) for other forbidden foods, reconciling various biblical verses and Talmudic discussions.
Source: Shu"t Chasam Sofer Collected §63