Question: This suggests that there is an Isur de'Rabbanan, as implied by the Lashon, in which case how can he be Mekadesh with it ...

Source: ... Did Rav not say in the first Perek of Pesachim (Daf 7a) that 'Someone who is Mekadesh from six hours and onwards, even with hard Chametz, which is only Asur mi'de'Rabbanan, we do not contend with his Kidushin?

answer #1: There, at least, it is in a time which is d'Oraysa, according to Rabeinu Tam there, whereas here it is entirely de'Rabbanan.

Answer #2: And according to Rashi as well, the Kashya falls away in the Maskana, that even according to Rebbi Shimon she is not Mekudeshes.

Clarification: The obligation to burn them is clearly d'Oraysa ...

Source: ... as is evident in Perek Kisuy ha'Dam (Chulin, Daf 85b), where it says 'If Chulin she'Nishchatu ba'Azarah is d'Oraysa, we can understand why we decree Chayah on account of Beheimah', which is why the Tana states "And the same applies to Chayah" ' ...

Clarification (cont.): ... but if you say that it is not d'Oraysa, how can he state "And the same applies to Chayah"? It (Beheimah) is only de'Rabbanan, will we decree (a Rabbanan on a de'Rabbanan)?'

Introduction to Question: How is this 'Sh'nei Kesuvim ha'Ba'im ke'Echad', since one cannot learn Shevi'is from Avodas Kochavim? ...

Question: Because one can ask 'Whereas Avodas Kochavim is Asur be'Hana'ah ... ?'

Answer: Nevertheless, let it write Shevi'is, and we could learn Avodas Kochavim from it.

Proof: And similar cases are often referred to as 'Sh'nei Kesuvim ha'Ba'in ke'Echad', and it is not necessary to learn each one from the other.

Introduction to Question: The question remains however, that had the Torah not written Avodas Kochavim, we would not have been able to learn it from Shevi'is, since they are not similar ...

Question #1: ... because by Shevi'is, the Kedushah always attaches itself to the last article and the previous one goes out to Chulin, whereas regarding Avodah Zarah, according to one opinion in Avodah Zarah (Daf 54b), all the articles remain forbidden? ...

Question #2: And even according to the opinion that the exchange of the exchange is permitted, it is still not similar to Shevi'is - where the last one does take effect (See Tosfos ha'Rosh)?

Answer: When the Torah writes (in Devarim, 7) "Vehayisa Cherem Kamohu" (See Hagahos ve'Tziyunim), it comes to teach us that Avodas Kochavim and Shevi'is are 'Sh'nei Kesuvim ha'Ba'im ke'Echad'.

Refutation of Question: It cannot be coming to teach us the Din itself - that Chalipei Chalipin are permitted ...

Reason: ... since we already know that from the Pasuk there "Ki Cherem Hu" - implying that it only makes Kadosh like itself once.

Explanation #1: Putrid water, Rashi explains.

Refutation: His explanation however, is unnecessary ...

Explanation #2: ... since one can explain it literally as 'cave-water' - water that has been gathered and is not from a spring, whereas we require spring water.

Explanation #2 (cont.): 'And his Eifer (Parah) is plain ashes' means that he contravened the command of the Torah, which writes (in Devarim, 4) "See, I have taught you Chukim and Mishpatim ... " - 'Just as I taught you free of charge, so too, should you teach free of charge.

Explanation #2 (concl.): Consequently, the one who taught for remuneration transgressed the Torah's command

Conclusion: We do not however, actually learn it from there, since the Pasuk does not indicate that someone who does teach for remuneration is not Yotzei ...

Conclusion (cont.): ... and to say that one is not is merely an Asmachta.

Question: What is the Chidush here? Why is it not obvious?

Introduction to the Chidush: It speaks in a case where, at the time of the Kidushin, the Shali'ach said to the woman 'So-and-so sent me to betroth you', before continuing 'Harei At Mekudeshes Li' - and she was aware that he betrothed her himself, otherwise the betrothal would not be valid.

The Chidush: And it teaches us that - although we may have thought that when he said 'Li', he was speaking in the name of the sender, that is not the case.