just like Pesach requires [one to] sleep overnight [“lina” in the city of Jerusalem on the first night of the holiday], so too Sukkot requires [one to] sleep overnight [in Jerusalem].

And there, how do we know [Pesach requires lina]?

As it is written (Deuteronomy 16:7), “and you shall turn in the morning, and go to your tents” [implying you had slept in the city that night].

The Tanna Kamma and Rabbi Shimon ben Elazar, what is their source for being able to make up for Shavuot?

It is learned out for them from that which Rabbah bar Shmuel taught,

as Rabbah bar Shmuel taught:

The Torah says that one should count the days and sanctify the [new] month, and says one should count the days and sanctify Shavuot [we can make a connection]. Just like the month [has a make up period] according to its counting [of day by day], so Shavuot [has a make up period] according to its counting [of week by week].