Question: I know only Achos Ishto. What is the source for other Arayos?

Answer #1 (R. Ze'irah citing R. Yosi ben Chaninah): Achos Ishto is Ervah with a Heter after her Isur (she is permitted after her sister dies). All other Arayos, which have no Heter after their Isur, all the more so Yibum is forbidden!

Just like this Ervah exempts her Tzarah, so other Arayos exempt their Tzaros.

Question: This is according to R. Akiva [who holds that Chayavei Lavim are exempt from Yibum or Chalitzah]. According to R. Yishmael [who obligates Chayavei Lavim to do Chalitzah, he must have another source!]

Answer #2 (R. Yishmael): we learn from a Kal v'Chomer. Achos Ishto is Ervah for which one is liable Kares for Mezid and Chatas for Shogeg, and she is forbidden to do Yibum. Also all Arayos that have Kares for Mezid and Chatas for Shogeg, she is forbidden to do Yibum.

Question: What is the difference between them?

Answer: They argue about a widow to a Kohen Gadol. The one who says Ervah with a Heter after her Isur, since she (a widow) has no Heter after her Isur, she is forbidden to do Yibum The one who says Ervah for which one is liable Kares for Mezid and Chatas for Shogeg, since she (a widow) is not liable Kares for Mezid and Chatas for Shogeg, she may do Yibum.

(R. Eibo bar Nagri Krispi citing Reish Lakish): "Lo Sihyeh Eshes ha'Mes ha'Chutzah l'Ish Zar" - a woman who is foreign (forbidden to) him may not be a wife for him, even for a Mitzvah (Yibum).

Question: If so (the Parshah excludes her), she should not need Chalitzah! (A Mishnah below teaches that she needs Chalitzah!)

Answer (R. Yirmeyah): It says "Yevimto" twice [at the beginning of Parshas Chalitzah, and one of them is totally extra] - the Torah included [Chayavei Lavim].

Question: If the Torah included through Yevimto... Yevimto, she should do even Yibum!

Answer (R. Yishmael): "Me'en Yevami" (he does not want to do Yibum), and not that Shamayim does not want.

Question: If so, she should not need Chalitzah!

Answer: For this we need R. Yirmeyah's Drashah "Yevimto... Yevimto" [in Parshas Chalitzah] - the Torah included [Chayavei Lavim] for Chalitzah.