Eruvin 11A

איפכא מאי?

The Talmud asks: What is the halakha in the opposite situation? Does an opening in the form of a doorway also serve to permit carrying in an alleyway that is more than 20 cubits high?

תא שמע דתניא: מבוי שהוא גבוה מעשרים אמה ימעט, ואם יש לו צורת הפתח אינו צריך למעט.

The Talmud answers: Come and hear the answer to this question, as it was taught in a baraita: If the cross beam placed over the entrance to an alleyway is higher than 20 cubits, one must diminish its height, but if the entrance has an opening in the form of a doorway, he need not diminish it.

אמלתרא ברחבו מאי? תא שמע, דתניא: מבוי שהוא גבוה מעשרים אמה ימעט, והרחב מעשר ימעט, ואם יש לו צורת הפתח אינו צריך למעט, ואם יש לו אמלתרא אינו צריך למעט.

The Talmud asks: What is the effect of a cornice with regard to the need to diminish the alleyway’s width? Does the cornice render the alleyway fit for one to carry within it, even if the entrance is more than 10 cubits wide? The Talmud answers: Come and hear an answer as it was taught in a baraita: If the cross beam placed over the entrance to an alleyway is higher than 20 cubits, one must diminish its height, and if the alleyway is wider than 10 cubits, one must diminish its width. However, if the entrance to the alleyway has an opening in the form of a doorway, he need not diminish it, and, similarly, if it has a cornice, he need not diminish it.

מאי לאו אסיפא: לא, ארישא.

The Talmud explains the proof it wishes to adduce from this baraita: What, is this statement with regard to the cornice not referring to the latter clause, i.e., the case of an alleyway that is wider than 10 cubits, proving that a cornice can render an alleyway otherwise too wide fit for one to carry within it? The Talmud refutes this argument: No, this statement is referring to the first clause of the baraita, that a cornice is effective for an alleyway more than 20 cubits high, but it tells us nothing about one that is more than 10 cubits wide.