Commentary for Bava Batra 4:3

A division: The splitting of a courtyard, such that they were in agreement about the splitting. And it is when there is not enough [room] for there to be eight ells for this one and for that one, such that one may not force his fellow to split it. And for this [reason], it taught that [it is if they wanted] - that since they want to split it, they build a wall of stones [even] against their will. And if one comes to say, "I do not want this expense, but rather [only] a mere bordermark," we do not listen to him, because of damage to visual privacy.

But say, "What is a mechitzah? A division": RI explains that it is because there are several difficulties with [understanding it as] a wall, as it challenges adjacently. Hence it forces it and explains a mechitzah as [being] a division - even though a mechitzah is a wall in every [other] place.

And since they wished [to divide the courtyard], they build a wall in the center [even] against his will: Later it is established [that this is a case] not subject to the law of division. But this is surprising to RI: As why did the teacher of our mishnah take [a case] not subject to the law of division, and teach, "who wished?" He should [more simply] speak about [a case] subject to the law of division. And he answered that we learn to deduce that I might have [otherwise] said that when it is not subject to the law of division, he would find to say, "It was on condition not to make a [bona fide] wall. I did not concede to you to make a wall." And there are some texts that explicitly ask and answer this at the end of the discussion.