Reference for Eruvin 27:15

מהו דתימא במינה אמרינן שלא במינה לא אמרינן קמ"ל:

R'Jose son of R'Judah holds [that it is valid] only within, but not above twenty cubits. R'JUDAH RULED: [THE BEAM IS VALID IF IT IS SUFFICIENTly] WIDE, ALTHOUGH IT IS NOT STRONG.

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