Question: Why did the Gemara not bring a proof from a woman who has relations with someone who is Pasul to her, who was not formed ba'Aveirahr, yet she is Pasul? ...

Question (cont.): ... and if one counters that the woman who has relations with someone who is Pasul is a stranger to her from the outset (See Yevamos 69a) -we can bring a proof from his children, and so the Din goes from one to the other ... ' ? ...

Answer: Perhaps they do not have a common factor or there is some other Pircha. (Tosfos Yeshanim).

Clarification: When the Gemara says 'different Sheimos' it is La'av Davka ...

Proof: ... seeing as someone who has relations with three Nidos in one He'elam (warning) is Chayav for each one, even though there is only one Shem - they all belong to the same husband

Source: ... as the Gemara says in K'risus (Daf 15a).

Clarification (cont.): So when it says 'three Almanos of three men' it is La'av Davka, since the same will apply to three Almanos of one man ...

Proof: And this is implied in the Gemara's answer 'But it speaks where he performed three Bi'os on one Almanah', and not that he had relations with the three Almanos of one man ...

Proof (cont.): ... implying that in such a case he will be Chayav three (sets of Malkos).

Question: Why will the Gemara shortly say that Rebbi Shimon does not hold 'Isur Chal al Isur'? Perhaps he doesn't hold 'Isur Chal al Isur', but he does hold of 'Isur Mosif'?

Proof: ... and this is an Isur Mosif regarding his sister, since initially she was Asur because of Achoso, and when she was widowed, the Isur Almanah was added [Seeing as it is an Isur Mosif regarding a Mashu'ach Milchamah who is not his brother] ...

Proof (cont.): ... since all women who are forbidden to the Kohen Gadol are also forbidden to the Mashu'ach Milchamah (Yoma 73a).

Answer #1: We learned in another Beraisa ((in Yevamos 32a) that Rebbi Shimon does not even hold of Isur Mosif.

Answer #2: Alternatively, the Gemara is saying that - since Rebbi Shimon does not hold 'Isur Chal al Isur' even a more stringent Isur on a more lenient one ...

Answer #2 (cont.): ... such as the case of someone who eats Neveilah on Yom Kipur, where the Isur of Yom Kipur does not take effect on that of Neveilah ...

Answer #2 (concl.): ... by the same token he will not hold of Isur Mosif by a more lenient Isur on a more stringent one, such as in the case of a Kohen Gadol who has relations with his sister who became an Almanah.