Reference for Eruvin 113:4

רב אשי אמר מאי רביע רביע דקרנות

Deduct a quarter from the measurements given<span class="x" onmousemove="('comment',' Sc. from the strip of open space around the town which, if square shaped, contains an area of eight million sq. cubits.');">⁴</span> and there would remain six [million square cubits];<span class="x" onmousemove="('comment',' The area of the city (1,000 X 1,000 sq. cubits) plus the area of the open space (a strip of a thousand cubits in width on the four sides of the town) amounts to 3,000 X 3,000 = 9,000,000 sq. cubits, when the city, and the open space around it are square shaped. When they are circular the total of their area amounts to 9,000,000 X 1/4 sq. cubits. The area of the open space alone amounts, therefore, to 9,000,000 X 3/4 - 1,000,000 X 3/4');">⁵</span> and six [million] represent a quarter of twenty-four [million].<span class="x" onmousemove="('comment',' The latter figure representing the total area of the limits of the land and the corners (v. supra 56b ad fin) which, unlike the open space, are not affected by the shape of the city.');">⁶</span>

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