Question: The Gemara loosely [and imprecisely] adopted the wording of the Mishnah in Horiyos that it brought above;

We know that one is liable a Chatas for Shogeg of Achos Ishah only from this Drashah!

Implied question: Why can't we learn from "Mitzvos-Mitzvos"?

Answer: "Kol Mitzvos" written regarding idolatry is needed, like the Sifri expounds;

"All Mitzvos" refers to idolatry, which is equivalent to all the Mitzvos.

Question: We should know this because it explicitly says Kares there, like Rabanan expound below!

Answer: Rebbi holds that that Kares is for blasphemy. It says "Es Hash-m Hu Megadef v'Nichresah";

In Pesachim (93b), Rebbi holds that Megadef is cursing Hash-m.

Question: They should learn from the entire matter from Aleha, for a Gezeirah Shavah is given to be expounded for everything!

Answer #1: "Aleha" written regarding Achos Ishah and Chatas are not Mufneh. The one regarding Yibum is Mufneh.

Answer #2 (R. Tam): Even if Aleha of Achos Ishah is Mufneh, since that of Chatas is not, we abandon a Gezeirah Shavah Mufneh on one side, and expound from what is Mufneh on both sides, like we say in Nidah 22b.

Question: Why don't we say "just like one is Chayav Skilah for idolatry b'Mezid..."?

Answer: We learn only from what is written in that verse. It mentions only Kares. The Tana holds that Megadef is serving idolatry;

Similarly, Rabanan do not say "just like idolatry has a Lav with Kares..." They do not require a Lav, since it is not written in that Parshah.

Proof: In Makos (13b), we exclude Pesach and Milah [from Chatas] because we require similar to idolatry, in which the Torah said "do not do", and these (Pesach and Milah) are fulfilled actively;

We do not exclude them because they do not have a Lav, unlike idolatry.

Distinction: However, according to Rebbi, who learns Chatas from Aleha, he requires a Lav with Kares, like Achos Ishah.

Support: In Shevu'os (13a), Rebbi expounds that Porek Ol (one who casts off the yoke of Shamayim), Mefer (annuls the) Bris and Megaleh Panim (distorts Torah) have Kares, but he does not list them among the 36 Kerisus (Kerisus 2a), for they do not have a Lav.

Explanation: They hold that there is no Kares for Porek Ol, Mefer Bris and Megaleh Panim;

Rather, they establish these three Kerisus for idolatry (Sanhedrin 64).

Explanation: He holds that since the Torah distinguished them (people of an Ir ha'Nidachas) from every other Chiyuv Misas Beis Din, in which the sinner's money is spared, we distinguish them regarding Kaparah (for Shogeg).

Question: Why don't we say that they bring a male lamb or ram?

Even if there is someone who brings it for Kaparah, the Gemara should have asked this! (Tosfos ha'Rosh - we ask only about what we find brought for a Chatas. We cannot fabricate a new Chatas. Aruch l'Ner - why was Tosfos unsure about a male lamb or ram? It is clear that there is no such Chatas in the Torah! He was unsure if it suffices that these are brought for an Asham, which also is for atonement.)

Observation: Everywhere, it is clear to the Gemara that R. Akiva, who says that Kidushin does not take effect on Chayavei Lavin, holds that Chayavei Lavin do not do Chalitzah or Yibum, just like Chayavei Kerisos.

We find this here, and below (79b) regarding a Petzu'a Daka and Krus Shafchah, and in Sanhedrin 53.

Question (Ri): Why don't we say also according to R. Akiva that Aseh Docheh Lo Sa'aseh [to permit Yibum of Chayavei Lavin]? (Tosfos ha'Rosh - perhaps he learns from a Hekesh equating Anusas Aviv, which is Chayavei Lavin, to Eshes Aviv, who is exempt from Yibum and Chalitzah.)

Explanation: We must say that both [sisters] were [born through] rape. (Whenever we mention rape, the same applies to enticement, or a marriage uprooted due to Kidushei Ta'os.)

If Reuven raped [the sisters' mother] and Shimon married her, both [daughters] are forbidden to Shimon. One is forbidden [even] because she is Shimon's daughter, and the other is forbidden [only] because she is his wife's daughter.

Source: "Regarding all of them I apply" connotes cases that occur often.

Observation: Below (28a), we ask that we find this also with [only] five brothers.