Reference for Bava Batra 165:2

ותני עלה ד' אמות שאמרו כדי עבודת הכרם אמינא ש"מ כמלא בקר וכליו ד' אמות

unless he has kept at a distance of four cubits:<span class="x" onmousemove="('comment',' Supra 18a; 26a. ');">³</span> and in connection with this it has been taught: 'The four cubits mentioned are the dimensions of the space required for attending to the vineyard': I concluded that the 'space of a pair of oxen and their outfit' is four cubits. But is there not also a Mishnah which agrees with [the report of] R. Joseph? Surely<span class="x" onmousemove="('comment',' For this reading, cf. BaH, a.l. ');">⁴</span>

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