Explanation #1: Rashi establishes it by a Penuyah, as the Gemara will do shortly, whereas 'Ein Osrin al ha'Yichud ' he establishes by a married woman.

Question: In that case the Mishnah is speaking li'Tzedadin (in two diferent cases)?

Explanation #2: We must therefore explain that the Seifa also speaks about a Penuyah, and it is referring to forbidding her to marry a Kohen because of Zonah.

Introduction to Question: There is a Kashy on this however, from the case in the Mishnah in the first Perek of Kesuvos (Daf 13a) 'She was seen 'talking with a man ... , and when they asked her about him, she replied that his name was so-and-so and that he was a Kohen. Rebbi Yehoshua holds that she is not believed' ...

Introduction to Question (cont.): ... and in reply to the query from Rav in our Sugya, who holds 'Ein Osrin al ha'Yichud', the Gemara answers 'Ma'alah Asu be'Yuchsin' ...

Question: Now according to what Tosfos just explained that it speaks about forbidding her to a Kohen, the Gemara's answer is meaningless, seeing as it speaks here specifically about Yuchsin, yet Rav says 'Ein Osrin ... '?

Answer: It does indeed speak about Yuchsin, and the Gemara there says 'Ma'aleh Asu be'Yuchsin' since she is not believed - because she admitted that she had relations with him ...

Answer (cont.): ... whereas here Rav says 'Ein Osrin', because she denies having had relations with him.

Refuted Explanation: Rashi explains 'Ein Chosh'shin' to give Malkos - implying that at least it is prohibited.

Refutation: In that case, what does the Gemra mean when it queries Rav Yosef shortly when he said 'Remove the ladder from underneath Bibi!'?, in view of Rabah's ruling - 'Ba'alah be'Ir, Ein Chosh'shin mishum Yichud'?

Refutation (cont.): What is the problem, seeing as there is no Malkos, but a prohibition there is?

Authentic Explanation: We must therefore explain that 'we are not concerned at all about Yichud, and that there is not even an Isur.

Clarification: This is the weak spot of the year regarding Yichud and immoral behavior.

Explanation: This refers to all the days of Yom-Tov, when groups of men and women gather to listen to the D'rashah (Yarchei Kalah), and they glance at one another.

Halachah: Some commentaries explain that this is the reason for the Minhag to fast after Pesach and after Sukkos.

Clarification: These Amora'im clearly acted le'Chumra ...

Halachah: ... whereas we Pasken like the Rabbanan of Rebbi Yehudah (further on, on Daf 82a) who maintain that 'Yisrael are suspected neither of homosexuality nor of bestiality.