Eruvin 33B

ורבי סבר לה כרבי מאיר, וסבר לה כרבי יהודה.

And R' Yehuda HaNasi holds in accordance with the opinion of R' Meir, and he also holds in accordance with the opinion of R' Yehuda.

סבר לה כרבי מאיר, דאמר חוקקין להשלים.

The Talmud clarifies: He holds in accordance with the opinion of R' Meir, who said the following in the case of an arched gateway in which the lower, straight-walled section is 3 handbreadths high, and the entire arch is 10 handbreadths high: Even if, at the height of 10 handbreadths, the arch is less than 4 handbreadths wide, one considers it as if he carves out the space to complete it, i.e., the arch has the legal status as though it were actually enlarged to a width of 4 handbreadths. Similarly, in our case the basket is taken into account and enlarges the tree to a width of 4 handbreadths.

וסבר לה כרבי יהודה, דאמר בעינן עירוב על גבי מקום ארבעה, וליכא.

And he also holds in accordance with the opinion of R' Yehuda, who said: We require that the eiruv rest on a place that is 4 by 4 handbreadths wide, and here there is not a width of 4 handbreadths without taking the basket into account.

מאי רבי יהודה? דתניא: רבי יהודה אומר: נעץ קורה ברשות הרבים והניח עירובו עליה, גבוה עשרה ורחבה ארבעה ⁠— עירובו עירוב, ואם לאו ⁠— אין עירובו עירוב.

The Talmud now asks: What is the source of the ruling of R' Yehuda? As it was taught in a baraita that R' Yehuda says: If one stuck a cross beam into the ground in the public domain and placed his eiruv upon it, if the cross beam is 10 handbreadths high and 4 handbreadths wide, so that it has the status of a private domain, his eiruv is a valid eiruv; but if not, his eiruv is not a valid eiruv.