Rif Shabbat 49a {Shabbat 125b}

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49a

{Shabbat 125b}
IF A [VINE-]BRANCH IS TIED TO A PITCHER {to let it down into the well}, ONE MAY DRAW [WATER] WITH IT ON THE SABBATH.

AS FOR THE STOPPER OF A SKYLIGHT, R. ELIEZER SAID: WHEN IT IS FASTENED {by a cord to the wall} AND SUSPENDED {in the air, the cord being too short to allow it to reach the ground}, ONE MAY CLOSE [THE SKYLIGHT] WITH IT; IF NOT, ONE MAY NOT CLOSE (THE SKYLIGHT] WITH IT.
BUT THE SAGES MAINTAIN: IN BOTH CASES WE MAY CLOSE [THE SKYLIGHT] WITH IT.

Gemara:
{"IF A [VINE-]BRANCH IS TIED TO A PITCHER":} If it is tied, yes, but if it is not tied, no, as a decree lest he cut {i.e., shorten} it.

"R. ELIEZER SAID: WHEN IT IS FASTENED...":
Rabba bar Rav Channa cited Rabbi Yochanan: All agree that we may not make for the first time a temporary building on a Yom Tov, and it goes without saying, on Shabbat. They differ only in respect of adding [to a building]: Rabbi Eliezer holds that we may not add on a Yom Tov whilst on Shabbat it goes without saying; whereas the Sages rule: We may add on Shabbat, and one need not say, on Yom Tov.

{I did not see the following in our gemara}
A brayta also says so: All agree that we may not make for the first time a temporary building on a Yom Tov, and it goes without saying, on Shabbat. They differ only in respect of adding [to a building]: Rabbi Eliezer holds that we may not add on a Yom Tov whilst on Shabbat it goes without saying; whereas the Sages rule: We may add on Shabbat, and one need not say, on Yom Tov.

"BUT THE SAGES MAINTAIN: IN BOTH CASES WE MAY CLOSE [THE SKYLIGHT] WITH IT":
What is meant "in both cases?"
Rabbi Abba bar Kahana said: