Eruvin 79B

ותבן שבעה ומשהו, דכל פחות משלשה כלבוד דמי.

and the hay in the house is slightly more than 7 handbreadths high it is considered a full-fledged partition that reaches the ceiling, as objects separated by any gap of less than 3 handbreadths are considered joined, based on the principle of lavud.

בשלמא לאביי, היינו דקתני ״מעשרה״, אלא לרב הונא בריה דרב יהושע מאי ״מעשרה״?

The Talmud comments. Granted, according to the opinion of Abaye, that is why the baraita teaches: If the height of the haystack was reduced to less than 10 handbreadths. However, according to Rav Huna, son of Rav Yehoshua, what is the meaning of: Less than 10? Even at the outset it was never as high as 10 handbreadths.

מתורת עשרה.

The Talmud answers: It means that it was reduced to less than the law of 10 handbreadths. As long as the hay is slightly more than 7 handbreadths high, it is regarded as 10 handbreadths high, in accordance with the principle of lavud. Once its height is reduced to less than 7 handbreadths, the halakha of a partition 10 handbreadths high is no longer in effect.

שניהן אסורין. שמע מינה דיורין הבאין בשבת אסורין?

The same baraita taught that if the height of the hay was reduced to less than 10 handbreadths, it is prohibited to carry in both. The Talmud comments: Should we learn from this that residents who arrive on Shabbat prohibit the other residents from carrying? At the onset of Shabbat, both sets of residents were permitted to use the hay and the house, but once the hay was reduced on Shabbat it is as though new residents had been added to each of the courtyards, and it is prohibited for all of them to carry. Why not say that since at the beginning of Shabbat it was permitted to carry in the domain, they are permitted to do so for its duration?