(Mishnah) Question: What is the Mitzvas Aseh about Nidah for which [the Great Sanhedrin] is liable [for a mistaken Hora'ah]?

Answer: If one was having Bi'ah with a Tehorah, and she told him "I became Tamei", if he withdrew the Ever immediately (amidst erection), he is Chayav [Kares], for withdrawing it is pleasurable, just like inserting it. (Rather, he may not withdraw it until the erection ceases.)

(Gemara - Kahana) Question: (A Mishnah in Horiyos says that there is no Asham Taluy for Tum'as Mikdash v'Kodoshav. What is the reason?) Is it impossible to have Yedi'ah at the beginning and the end and Helam in between?!

Note: R. Shmuel thought that Kahana questions why the Mishnah exempts the Sanhedrin for Hora'ah about Tum'as Mikdash v'Kodoshav, therefore he asked the following question.

Question (R. Shmuel bar Avadumi, to R. Mana): Can we find this regarding tbose (the Sanhedrin) who rule?! (Helam Tum'ah in the middle does not apply to them. Our Mishnah properly exempts them!)

Answer (R. Mana): We (Kahana) question why people who enter [are exempt from Asham Taluy]. Do you bring us [a reason to exempt] those who rule?!

Question: What is the reason [why people who enter are exempt from Asham Taluy]?

Answer (R. Shmuel bar Rav Yitzchak): We learn from a Gezeirah Shavah "Mitzvos-Mitzvos" - just like Mitzvos said below [regarding Par Helam Davar] refers to [Aveiros for which an individual brings a Chatas] Kavu'a (not Oleh v'Yored), also here (Asham Taluy applies when an individual brings Chatas) Kavu'a. (We explained this like KORBAN HA'EDAH.)