Commentaire sur Bava Batra 1:4
כֹּתֶל חָצֵר שֶׁנָּפַל, מְחַיְּבִין אוֹתוֹ לִבְנוֹתוֹ עַד אַרְבַּע אַמּוֹת, בְּחֶזְקַת שֶׁנָּתַן, עַד שֶׁיָּבִיא רְאָיָה שֶׁלֹּא נָתָן. מֵאַרְבַּע אַמּוֹת וּלְמַעְלָה, אֵין מְחַיְּבִין אוֹתוֹ. סָמַךְ לוֹ כֹתֶל אַחֵר, אַף עַל פִּי שֶׁלֹּא נָתַן עָלָיו אֶת הַתִּקְרָה, מְגַלְגְּלִין עָלָיו אֶת הַכֹּל, בְּחֶזְקַת שֶׁלֹּא נָתַן, עַד שֶׁיָּבִיא רְאָיָה שֶׁנָּתָן:
Si un mur de cour [des partenaires] tombe, il (c'est-à-dire chacun des partenaires) est tenu de le reconstruire jusqu'à (une hauteur de) quatre coudées, [cela suffit pour éviter les «dommages causés par l'observation»]. Il est réputé avoir donné à moins qu'il ne soit prouvé qu'il n'a pas donné. [c.-à-d. si l'un réclame la moitié des dépenses et l'autre dit qu'il a déjà donné sa part, on le croit, à moins que le demandeur ne puisse amener des témoins qu'il a réclamés et que l'autre n'a pas donné. Car tous savent que chacun doit donner sa part, et que l'autre n'aurait pas construit seul (sans que le premier ait contribué), mais il l'aurait amené à Beth-Din.] De quatre coudées et plus, il (le second) est non obligatoire (pour la moitié de la hauteur supplémentaire). S'il y a accolé un autre mur, même s'il ne l'a pas couvert, tout lui est imposé. [c'est-à-dire, si après le premier construit bien au-dessus de quatre coudées et que le second ne voulait pas l'aider, il (le second) y attachait un autre mur afin de le couvrir de mur en mur— même s'il ne l'avait pas encore couvert, tout lui est imposé, ayant fait comprendre qu'il privilégie la hauteur supplémentaire.]
Bartenura on Mishnah Bava Batra
English Explanation of Mishnah Bava Batra
[If the fence was built] four cubits or higher, they do not obligate him [to help in building it.] If [the one who did not contribute] built another wall near it, even if he did not put a roof upon it, they obligate him to share in all of the costs. He is presumed not to have paid [his share] unless he brings proof that he has.
Mishnah four continues to discuss a wall built in a courtyard owned by two partners, a topic that began in the first mishnah of the chapter.
In the times of the mishnah, a standard wall, built in a courtyard was about four cubits high (over two meters, a little less than seven feet). Therefore, if the previous wall fell down, each partner would be obligated to rebuild the wall until it was four cubits high. If Reuven claims that Shimon did not pay his share, Reuven must bring proof. Since this law is commonly known, we assume that Reuven would not have begun to build the wall until Shimon paid his share. If he did build the wall without first collecting, he must bring proof that Shimon still owes him money.
In contrast, if Reuven built the wall over four cubits, he cannot ask Shimon to pay for the costs of the added height. Since walls are not commonly built over four cubits high, Shimon can claim that he did not want such a high wall. If however, Shimon were to use the wall to support another wall, and show that he intended to lay a roof on the two walls, he must pay for the added height. Although he was not initially obligated, since he subsequently used the wall, he is obligated to pay for it. Since this law is not commonly known, we cannot assume that Shimon paid his share. Until he brings a receipt showing that he has paid for the wall, he will still be obligated towards Reuven.