Bava Batra 102 - Shabbat Shuva - October 5, 3 Tishrei

A Mishna is brought from Ohalot and Nazir which seems to have measurements of burial caves that don't match either Tanna Kamma or Rabbi Shimon's opinions in our Mishna. The Gemara tries to figure out how to connect the opinion in the Mishna with one of the two opinions. If someone sells a field and specifies the size but some of the field is not worthy of planting, is that space included in the size of the field? On what does it depend?