Responsa for Bava Batra 34:2

אמר אביי ואיתימא רב יהודה מכותל בורו שנינו

— The use of the word WALL teaches us that the wall of the pit must itself be three handbreadths thick.<span class="x" onmousemove="('comment',' Because we understand the Mishnah to mean, 'he must keep the hollow of his pit three handbreadths from the side of the other's pit', i.e., three from the boundary, which are filled by the side of his own pit. This is the explanation of Rashi, and is apparently forced. Tosaf, greatly simplifies the passage by omitting the sentence, 'But still why&nbsp;… neighbour's pit' (or, alternatively, by inserting it after 'speaking of his wall'). The explanation would then be as follows: Abaye says that he must keep his pit three handbreadths from the side of his neighbour's pit (which presumably comes up to the boundary), and we infer from this that the neighbour also must not dig his pit close up to the boundary; whereas if the word 'pit' had been used, we should not have been able to infer this. ');">²</span>

Teshuvot Maharam