Shabbat 6B

לחי מכאן, ולחי מכאן, או קורה מכאן וקורה מכאן, ונושא ונותן באמצע. אמרו לו: אין מערבין רשות הרבים בכך!

a 10-handbreadth high post from here, perpendicular to the public domain. This creates a symbolic wall which, in the halakhot of alleyways, has the legal status of a wall. And, he may place an additional post from here, on the other side, and that has the same legal status as if he closed the public domain on all of its sides. Or, he can implement a different solution appropriate for alleyways by placing a beam extending from here, from one end of one house, to the end of the house opposite it. This creates a symbolic partition across the width of the street. And, he may place a beam extending from here, from the other side of the house. According to R' Yehuda, in that way, one is permitted to carry objects and place them in the area between the symbolic partitions, as he would in a private domain. The Rabbis said to him: One may not place an eiruv in the public domain in that way. One who seeks to transform a public domain into a private domain must erect actual partitions.

ואמאי קרו ליה ״גמורה״? מהו דתימא: כי פליגי רבנן עליה דרבי יהודה דלא הוי רשות היחיד, הני מילי לטלטל, אבל לזרוק מודו ליה ⁠— קא משמע לן.

The Talmud questions the language of the Tosefta: This is a full-fledged private domain. And why did they call it full-fledged? The Talmud answers: Lest you say: When do the Rabbis disagree with R' Yehuda and say that it is not the private domain? This applies only with regard to the prohibition to carry there on Shabbat. By means of these partitions, it was not rendered a full-fledged private domain to the point that one is permitted to carry there. However, conceivably, with regard to the prohibition of throwing from the public domain to this place, the Rabbis agree with R' Yehuda that the area between the partitions would be considered a private domain by Torah law and it would be prohibited. Therefore, the tanna taught us that according to the Rabbis it is not a private domain at all.