מי דמי התם נעשה בסיס לדבר המותר הכא נעשה בסיס לדבר האסור אלא הכי קאמרי ליה אם מצילין תיק של ספר עם הספר ואף על פי שיש בתוכו מעות לא נטלטל עור אגב בשר מי דמי התם נעשה בסיס לדבר האסור ולדבר המותר הכא כולו נעשה בסיס לדבר האסור אלא הכי קאמרי ליה אם מביאין תיק שיש בתוכו מעות מעלמא להציל בו ספר תורה לא נטלטל עור אגב בשר

The Gemara asks: Are they comparable? There, with regard to the Torah scroll, the casing is a base for a permitted object, i. e., the scroll itself, which may be moved on Shabbat; whereas here, with regard to the hide of the Paschal lamb, the skin is a base for a prohibited object, i. e., the flesh of the sacrifice, which may not be moved until nightfall because it may not be eaten until night. Rather, this is what they said to him: If one may save the casing of the Torah scroll along with the scroll, even if there is money inside it, why then may one not move the hide together with the flesh? The Gemara asks: Are they comparable? There, with regard to the Torah scroll, the casing becomes a base for a prohibited object and a permitted object; whereas here, with regard to the hide, it is entirely a base for a prohibited object. Rather, this is what they said to him: If one may bring a casing that has money inside it from outside in order to save a Torah scroll in it, why may one not move the hide together with the flesh?

והיא גופה מנלן אילימא דמדהיכא דאית ביה לא שדי להו איתויי נמי מייתינן מי דמי התם אדהכי והכי נפלה דליקה הכא אדהכא והכי לישדינן אלא אמר מר בר רב אשי לעולם כדאמרינן מעיקרא ודקא קשיא לך הכא טלטול והכא מלאכה כגון דלא קבעי ליה לעור

The Gemara asks: And from where do we derive this halakha itself? As it is not stated in the mishna, from where do we derive that it is permitted on Shabbat to bring a casing containing money from the outside in order to save a Torah scroll? If you say that from the fact that in a situation where the casing has money in it one does not throw it away but brings it out with the casing, when the casing is outside and has money in it, one may also bring the money along with it; is it comparable? There, with regard to the Torah scroll’s casing with money inside, if one tarries in order to empty the money from the case, in the meantime the fire might catch the Torah scroll and burn it; whereas here, with regard to bringing in the casing, in the meantime he could have thrown it away. Rather, Mar bar Rav Ashi said: Actually, it is as we said initially. The Sages equated carrying the Torah casing with flaying the hide of the Paschal lamb. And as for what was difficult for you, that here, with regard to the Torah casing, moving alone is involved, whereas here, with regard to a Paschal lamb, a prohibited labor is involved, it can be explained as referring to a case where one does not need the hide of the Paschal lamb. Therefore, he is exempt.

והא אביי ורבא דאמרי תרוייהו מודה רבי שמעון בפסיק רישיה ולא ימות דשקיל ליה בברזי:

The Gemara asks: But Abaye and Rava both said: Rabbi Shimon concedes in cases categorized as cut off its head and will it not die, i. e., an action with an inevitable consequence. When an action has an inevitable consequence, even Rabbi Shimon, who normally exempts a person for performing an action with an unintended consequence, maintains the one is liable. Rather, we must say that one flays it strip by strip, and thereby he does not benefit from the hide. It therefore does not constitute the prohibited labor of stripping the hide.

ולהיכן מצילין אותן וכו׳: היכי דמי מפולש היכי דמי שאינו מפולש אמר רב חסדא שלש מחיצות ושני לחיין זהו מבוי שאינו מפולש שלש מחיצות ולחי אחד זהו מבוי המפולש ותרוייהו אליבא דרבי אליעזר דתנן הכשר מבוי בית שמאי אומרים לחי וקורה ובית הלל אומרים או לחי או קורה רבי אליעזר אומר שני לחיים

We learned in the mishna: And to where may one rescue them? Into an alley that is closed, which, if it is surrounded on three sides, is considered to be a private domain by Torah law. Ben Beteira says: Even into an open alley. The Gemara asks: What are the circumstances of an alley that is open, and what are the circumstances of an alley that is not open? Rav Ḥisda said: An alley that has three walls and two posts at its entrance is an alley that is not open; one that has three walls and one post is an alley that is open. And they both, the first tanna and ben Beteira, disagree in the mishna in accordance with the opinion of Rabbi Eliezer, as we learned in a mishna: For preparation of an alley to permit carrying within it on Shabbat, Beit Shammai say the alley must have a post on the side of the entrance and a beam over the entrance. And Beit Hillel say: Either a post or a beam is sufficient. Rabbi Eliezer says: In order to permit carrying, two posts are required.

אמר ליה רבה שלש מחיצות ולחי אחד מפולש קרית ליה ועוד לרבנן נציל לתוכו אוכלין ומשקין אלא אמר רבה שתי מחיצות ושני לחיין זהו מבוי שאינו מפולש שתי מחיצות ולחי אחד זהו מבוי המפולש

Rabba said to him: Did you call an alley that has three walls and one post open? Even if Rabbi Eliezer does not permit carrying there, it is still not considered to be open but closed. And furthermore, according to the Rabbis, if this is so, let us rescue food and drinks by carrying them there as well. Since the Sages only permitted carrying in an alley that is not open, and because, according to all opinions, it is permitted to carry in a closed alley, one should also be allowed to save food and water, and not only a Torah scroll, by carrying them there. Rather, Rabba said: An alley that has two walls and two posts at both entrances to the alley is an alley that is not open. If it has two walls and one post, it is an alley that is open.

ותרוייהו אליבא דרבי יהודה דתניא יתר על כן אמר רבי יהודה מי שיש לו שני בתים בשני צדי רשות הרבים עושה לחי מיכן ולחי מיכן או קורה מיכן וקורה מיכן ונושא ונותן באמצע אמרו לו אין מערבין רשות הרבים בכך

And both of them hold in accordance with the opinion of Rabbi Yehuda. As it was taught in a baraita:

Furthermore, Rabbi Yehuda said: One who has two houses opposite each other on two sides of the public domain, if he chooses, he may create a private domain for himself in the area of the public domain. He may place a ten-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 Rabbi 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 establish an eiruv in the public domain in that way.

אמר ליה אביי לדידך נמי לרבנן נציל לתוכו אוכלין ומשקין

Abaye said to Rabba: According to your opinion too, according to the opinion of the Rabbis cited in the mishna who agree with Rabbi Yehuda and permit carrying in an alley that is closed, let us also save food and drinks by carrying them there.