Date: Shushan Purim 5564
From: Rabbi Moshe Sofer
To: Unknown recipient
A correspondent raises a mathematical difficulty with Tosfos on Pesachim 109a regarding the squared dimensions of the revi'is cup. The Chasam Sofer proposes a scribal error in Tosfos and demonstrates that the principle 'a square exceeds a circle by a quarter' applies to circumference, not area.
Source: Shu"t Chasam Sofer OC §153