Eruvin 78B

חקק להשלים בכותל, בכמה? אמר ליה: בעשרה.

Rav Yosef further asked: If the ladder resting against the wall was less than 4 handbreadths wide, and one dug out grooves in the wall as extensions of the rungs of the ladder to complete the measure, how high must this hollowed-out section be to consider the ladder a valid passageway between the two courtyards? Rabba said to him: If it is 10 handbreadths high and 4 handbreadths wide, it is considered a passageway.

אמר ליה: חקקו כולו בכותל, בכמה? אמר ליה: מלא קומתו. ומאי שנא? אמר ליה: התם מסתלק ליה, הכא לא מסתלק ליה.

Rav Yosef said to him: If there was no ladder, and one dug out the entire ladder in the wall, so that all the steps are grooves in the wall, how much must he hollow out? Rabba said to him: Those steps must reach the full height of the wall. Rav Yosef asked: And what is the difference in this case? Why must the steps reach higher in this case than in the case where the hollowed-out section was merely an extension of an existing ladder? Rabba said to him: There, where there is a ladder, it is easy to climb to the top of the wall; however, here, where there are only grooves in the wall, it is not easy to climb. If one cannot reach the top of the wall, the steps are not considered a passageway between the courtyards.

בעא מיניה רב יוסף מרבה: עשאו לאילן סולם, מהו?

Rav Yosef raised a dilemma before Rabba: If one designated a tree as a ladder, what is the halakha? Given that it is prohibited to climb a tree on Shabbat, if a tree stands next to a wall and it is easy to climb, is it considered with regard to the halakhot of Shabbat as an opening in the wall that can serve as a passageway between the two courtyards?