Explanation: To join to 10, we do not need the reason that he rests something on it. If the pit is four wide, but it is 10 deep only through joining the Chulya (ring of earth excavated from the pit piled up around it), it is an absolute Reshus ha'Yachid, and he uses it properly, since the walls of the pit from the middle are 10 tall;

The reason that he rests something on it, why should this help there, since the Chulya is not 10 tall from the outside?

This reason helps only when the pit [itself] is not four wide from the inside. It is four wide only through joining the Chulya, and the Chulya is 10 tall from the outside to Reshus ha'Rabim;

Even though the inside is not Reshus ha'Yachid, on [the Chulya] is Reshus ha'Yachid, for if he wanted, he could put something on it and use it.

Implied question: R. Yochanan mentioned only joining to 10!

Answer: Even so, [Rav Ashi] deduces from R. Yochanan's teaching, because R. Yochanan discusses the Mishnah (Shabbos 99a), like Rashi explained, that we learn from it also joining to four, for [the Mishnah] taught "and their width is four."

Question: Also regarding our Mishnah below (99b), R. Yochanan deduced so regarding a pit in Reshus ha'Rabim and its Chulya is 10 Tefachim tall, and R. Yochanan said in the Gemara "they can even be nearby. The Chidush is that a pit and its Chulya join to 10." Why are both of these needed?

Answer (Ri): The case in Shabbos is needed for joining to four, which is not taught below;

If not for the case below, from the case in Shabbos alone one could not deduce. One might have thought that Agav (along with) a rock, it mentioned the Chulya of a pit, for everywhere it normally mentions a Chulya along with a rock.

Explanation #1 (Rashi): [It is 14 because] he must withdraw the legs (bottom) of the ladder four Tefachim from the wall.

Rebuttal (and Explanation #2): He was not precise. Even if he withdraws it 10 Tefachim from the wall, which is the height of the wall, the end of the ladder will reach the top of the wall, for 14 is the size of the diagonal of 10 by 10, since for every Amah in [the side of] a square, the diagonal is one and two fifths Amos. Also R. Chananel explained like this.

Question: If you distance the legs of the ladder from the wall 10 Tefachim, and lean the top of the ladder on the wall, you are forced to say that the top of the wall will be more than a Tefach taller than the ladder according to Rav Yosef, and more than three Tefachim according to Abaye!

Source: If the ladder (whose legs are 10 from the wall) was [four Tefachim shorter, i.e.] only 10 Tefachim, in any case [the top would be] more than four Tefachim away [from the top of the wall], for the ladder would totally fall to the ground! (It reaches only to the bottom of the wall. Rashash - i.e. shortening the ladder four decreases its leaning height 10. Tosfos infers that the leaning height is always decreased more than the length of the ladder was decreased.)

Implied suggestion: Also according to Rav Yosef and Abaye, the top of the ladder leans on the top of the wall, just they put the legs of the ladder closer than according to Shmuel. According to Abaye, it is close to vertical.

Rebuttal: Why should they mention this Shi'ur (of 13 or 11)? And why did Rav Yosef and Abaye mention [and] Mashehu?

Answer (Ri): They said so for a mere Siman. Always, one must distance the ladder like its leaning height on the wall, and the height of the wall may not exceed the [leaning] height of the ladder more than a Tefach according to Rav Yosef, and three Tefachim according to Abaye, like the Shi'ur of Lavud;

According to Rav Yosef, it suffices Mashehu and 13 less two Chomshin, which is the diagonal of [a square] nine by nine;

According to Abaye, it suffices Mashehu and 10 Tefachim less a Chomesh, which is the diagonal of [a square] seven by seven.

Explanation: [Shmuel] said so according to Rav, but Shmuel himself holds that a vertical ladder does not diminish, for he requires a ladder 14 [Tefachim].

Explanation #1: Even though they do not have four rungs, their weight fixes them.

Explanation #2 (Rashbam): This is the Tzuri ladder mentioned above (77b).

Rejection #1: If so, it should not have said "ladders of Bavel"!

Rejection #2: Above, [it says that a Tzuri ladder diminishes, and] no one disagrees. Here, we say [according to Rabah] that ladders [of Bavel are] not [Mema'et, unless they are fixed].

Explanation: E.g. the wall is thick and protrudes on the side of the ladder, or the ladder rests in the end of the wall in the corner, and we discuss an inclined wall.

Source: Rav Yosef [cannot ask about a vertical ladder, for he] holds that a vertical ladder does not diminish, and he requires 13 and Mashehu, and here Rav Yosef asks!

Explanation #1 (Rashi): He completes it until 10. Even though the wall is higher, we are not concerned.

Question: He cannot go up [on the wall], since the wall is taller!

Answer: Granted, he carved into the wall only until 10. We are concerned only that the ladder reach the top of the wall.

Explanation #2 (R. Tam): "Ten" means that 10 [Tefachim] may not remain from the ladder until the top of the wall (Maharsha. Rashash - the ladder reaches until the top of the wall. There may not remain 10 from the top of what is carved until the top of the wall.)

Explanation: Rav Nachman bar Yitzchak argues with the Sugya above (31a), which connotes that according to everyone, one may not acquire a house (Shevisah) with Isurei Hana'ah, and here he says that they argue about whether one may acquire a house with Isurei Hana'ah.

Explanation: We discuss straw and stubble that may be moved on Shabbos, and unlike above (77a) "an unripe fig stored in straw."

Source: It says in the Gemara "a person is Mevatel even a wallet." (If the straw were Asur to move, all the more so it would be Batel!)

Question: We say that even Peros are Mevatel Mechitzos, for we say in Shabbos (100a) that a pit 10 [Tefachim] deep and four [Tefachim] wide full of water, and he threw into it, he is liable. If it is full of Peros and he threw into it, he is exempt;

Citation (100a): What is the reason? Water is not Mevatel a Mechitzah. Peros are Mevatel a Mechitzah.

Answer (Ri): Mid'Oraisa, surely [Peros] are Mevatel. However, for Eruv mid'Rabanan we can distinguish between what may be moved and what may not be moved.

Question: Below, we compare this to a house that one filled it, which pertains to [Tum'as] Ohel mid'Oraisa. Also from the case of Ohel we can challenge the teaching in Shabbos! (Since both are mid'Oraisa, the Ri's answer does not apply.)

Explanation #1 (Rashi): This is when he puts a plank four wide from one to the other. Also this is an opening.

Question: Since we discuss through a plank four wide, how does the Gemara (79a) deduce "only when they are opposite each other, but when they are not opposite each other, no"?

Even if they are far apart, they should be permitted through a plank four wide, like it says above (77b) "when the wall is four [wide], even if [the ladders] are far from each other" (for it is easy to walk on the wall from one to the other)!

Explanation #2 (R. Tam): We do not discuss when he put a plank from one to the other;

He gives to the balconies the law of a trench. If there are four [Tefachim] from one [side] to the other, they may be Me'arev separately, but they may not be Me'arev like one, like a trench;

However, if less than four [separate the sides], it is common to step from one to another, like regarding a trench, like it says in Shabbos (100b) regarding a puddle. If it is not four [wide], people step over it;

Therefore, when less than four separate the sides, they may be Me'arev separately, and if they want, they may be Me'arev like one, even if they are distanced three, when they are opposite each other.

Distinction: When they are not opposite each other, they may not be Me'arev together when they are distanced three, like it says in the Gemara. ["And less than this" in our Mishnah refers back to a plank.]

Remark: This is the text in all Seforim. Also R. Chananel explained like this.

Explanation (Ri): It is a Mishnah in Ohalos (15:7). It is not written there "straw", rather, earth or pebbles. Also, the text does not say there "if he was Mevatel it, it is Batel."

Citation (15:7 - Mishnah): If a house was filled with earth or pebbles, and he was Mevatel it, and similarly a stack of grain or a pile of pebbles, even like the pile of Achan, and even if Tum'ah is next to Kelim, the Tum'ah breaks through and ascends; it breaks through and descends.

The Gemara brings [the Mishnah] abbreviated. This is the Gemara's style in several places.

Suggestion: Perhaps what it brings here is a Beraisa!