Introduction to Question: Since the Gemara says 'Ho'il ve'Haysah lah Sha'as ha'Kosher', it implies that currently it is not subject to redemption?

Question: But why not? Seeing as Rebbi Shimon holds in Shevu'os (Daf 11b & 12a) that the Parah Adumah is Kodshei Bedek ha'Bayis ...

Question (cont.): And in the very same Sugya there, he holds that Kodshei Bedek ha'Bayis are not subject to Ha'amadah and Ha'arachah?

Answer: We therefore need to say that when the Tana says 'Ho'il ve'Haysah lah Sha'as ha'Kosher', it is speaking after the Haza'ah ...

Answer (cont.): ... and it is no logical to say that it can be redeemed after the blood has been sprinkled; nevertheless, it is Metamei Tum'as Ochlin, since it had a Sha'as ha'Kosher before the Haza'ah.

Question: Why do we not apply the principle 'Kol ha'Omed Lehazos, ke'Muzah Dami'?

Answer: Before the blood has been received in the Kos, it is not considered ke'Muzah, as Tosfos explained earlier (on the previous Amud, DH 'Kol').

Question: Rabeinu Chayim b'Rebbi Shmuel asks why it had to have a Sha'as ha'Kosher? Why do we not say that Chibas ha'Kodesh renders it 'Kasher' and turns it into a food ...

Question (cont.): ... as the Gemara explains in the second Perek of Chulin (Daf 36b & 37a) "ve'ha'Basar", 'to include wood and frankincense'?

Refuted Answer: And if you will say that 'Chibas ha'Kodesh' , according to Rebbi Shimon, is not applicable to Parah, since it is Kodshei Bedek ha'Bayis ...

Refuted Answer (cont.): ... because 'Chibas ha'Kodesh' is not even applicable to Kodshei Mizbe'ach, unless they are declared Kedushas ha'Guf inside a K'li Shareis, as is evident at the beginning of 'ha'Menachos ve'ha'Nesachim' (Menachos, Daf 101a) and in Perek Kol ha'Pesulin (Zevachim, Daf 34a) ...

Refutation: ... it is clear that 'Chibas ha'Kodesh' does apply to Parah, even according to Rebbi Shimon ...

Source: ... since the Gemara, at the beginning of 'ha'Menachos ve'ha'Nesachim' (Daf 102b) asks, why, according to Rebbi Shimon, Nosar and Parah, are Mitam'in Tum'as Ochlin, seeing as they are merely dust, seeing as whatever stands to be burnt is considered burned? ...

Source (cont.): ... and it answers that Chibas ha'Kodesh renders it 'Kasher'.

Reason: ... and the reason for this is because, even though it did not become sanctified by means of a K'li Shareis, 'Chibas ha'Kodesh' nevertheless applies, since the Torah calls it a 'Chatas' (Chulin, 11a).

Reason (cont.): ... and everything connected with it is like the Avodah of Kedushas ha'Guf (of a Chatas) - it is sprinkled and it is Pasul she'Lo li'Shemah.

Answer: The Ri answers that 'Chibas ha'Kodesh' is only effective to turn a non-food into a food - such as Nosar and Parah which are considered like dust, or wood and frankincense ...

Answer (cont.): ... but as for something that is already a food, but which is not Mekabel Tum'ah according to Rebbi Shimon, since it is not fit to feed to others (because it is Asur be'Hana'ah), Chibas ha'Kodesh will not help to render permitted something that is forbidden.

Question: And when the Gemara at the beginning of Kol ha'Pesulin thinks that, were it not for the fact that we include it from "ve'ha'Basar", to include wood and frankincense - someone who eats Basar that became Tamei before the Z'rikah would not receive Malkos, based on the D'rashah that whatever is not permitted to Tehorim, one is not Chayav on it because of Tum'ah ...

Answer: ... that is because, since the Gemara only wants to exempt it (Tum'as Basar) from Tum'as ha'Guf, we can include him from "ve'ha'Basar" via a Kal va'Chomer from Eitzim and Levonah.

Question: Why do we not say that all Kodshim are subject to Tum'ah in their lifetime, seeing as it is a Mitzvah to Shecht them, in which case we ought to say 'Whatever stands to be Shechted is considered Shechted'?

Answer: Even if it has been Shechted, we will not consider the blood to be 'Zaruk' until it has been received in a Kos, how much more so before it has even been Shechted.

Question: The Ri asks however, why the Sa'ir ha'Mishtale'ch is not Tamei Tum'as Ochlin in its lifetime, according to Rebbi Shimon, according to the opinion in Yoma (Daf 67a) that permits deriving benefit from its limbs ...

Reason: ... because, since it stands to be pushed down from the rock, it is considered pushed down'?

Answer: We only say that 'Something that stands to be done is considered done' to render a food that is forbidden, permitted, in that we now call it 'A food that one is able to feed others' ...

Answer (cont.): ... it does not however, help to turn something that is not a food, such as a living animal, into a food ...

Implied Question: Even though it would help to turn a food, such as Nosar or Parah, into dust, were it not for the fact that 'Chibas ha'Kodesh renders them 'Kasher' ...

Precedent: This is similar to a ben Peku'ah and fish, both of which are permitted without Shechitah, yet the fact that they are alive renders them Tahor ...

Precedent (cont.): ... according to the Rabanan who argue with Rebbi Yossi ha'Gelili' in Perek Beheimah ha'Mekasheh (Chulin, Daf 75a).

Question: Rashi, in Perek Oso ve'es B'no (Chulin, Daf 82a [See also Tosfos there, 81b DH 'Parah Metam'ah']) asks as to why it needs Kabalas Tumn'ah? Why the fact that it itself renders Tamei Adam and his clothes will not suffice?

Answer: And he answers that in similar vein, the Gemara in Kerisos (Daf 21a) says 'Such as where one covered less than a k'Beitzah (of Neveilah) with dough; If one renders it a food, it combines with the dough, which in turn, receives Tum'ah in the event that it touches Tum'ah, and which then renders other food Tamei as well.

Answer (cont.): But if it is not a food, then the dough is not subject to Tum'ah, since it does not have a Shi'ur, in which case, other food that touch it remain Tahor, seeing as they touch. not the Neveilah, only the dough' (Rashi).

Implied Question: The reason that he mentions Neveilah (and not Parah) is ...

Answer: ... because he is referring to the Sugya in K'risos.

Refutation: And what Rashi says that 'The dough receives Tum'ah if it touches Tum'ah', he said absentmindedly, the Ri explains, seeing as the case of 'Chipeihu be'Batzek' in K'risos is speaking where there is a k'Zayis of Neveilah.

Clarification: It therefore seems that the dough receives Tum'ah from the Neveilah, by virtue of the combination to make up a k'Beitzah (of food), just like it would if it received Tum'ah from somewhere else, since the K'zayis can render Tamei and combine at one and the same time.

Comment: Rashi also seems to have retracted from he was accustomed to saying in many places (See Pesachim, Daf 33b DH 'be'ke'Beitzah' & Zevachim Daf, 31a DH 'Letamei') that even food that is less than a k'Beitzah is subject to Tum'ah min ha'Torah ...

Comment (cont.): ... since he specifically explains that the dough is not subject to Tum'ah since it lacks the required Shi'ur.

Refuted Answer: One cannot answer Rashi's Kashya by saying that without the combination of the dough, one requires the reason of Sha'as ha'Kosher, since it is only those who are dealing with it who render their clothes Tamei ...

Support: ... as we learned in the Mishnah in Parah (8:3) 'The person who burns the Parah and the bulls (the Parim ha'Nisrafin), and the one who sends away the Sa'ir ha'Mishtale'ach render their clothes Tamei, even though they themselves (the Parah ...) do not render the clothes Tamei ...

Support (cont.): ... and they (the clothes) now say 'The one that rendered you Tamei, does not render me Tamei, but you do render me Tamei!'

Refutation: Since, in spite of that, it renders Tamei food and drink, seeing as eventually it stands to render those who deal with it a stringent Tum'ah, requiring neither Hechsher Mayim nor Hechsher Sheretz ...

Source: ... as Tana de'bei Rebbi Yishmael learns in a Beraisa in Perek Ba Si'man (Nidah, Daf 51a & 51b) - 'If already seeds, that do not stand to finally become a stringent Tum'ah, require a Hechsher ... '.

Answer: The Ri answers that, the fact that it stands to finally become a stringent Tum'ah is only effective in that it is as if it has become Huchshar via water or as if it touched a Sheretz, but not to turn a non-food into a food.

Answer (cont.): Consequently, according to Rebbi Shimon who requires a food that one can feed to others, standing to finally become a stringent Tum'ah will not achieve that.

Answer (concl.): And that explains why it is only Tamei because it had a Sha'as ha'Kosher.

Proof: And this is evident at the end of Perek T'vul Yom (Zevachim, Daf 105a) where Rebbi Meir, in a Beraisa, states that 'the clothes of the person who burns Parah, Parim and the one who sends the Sa'ir are Tamei, even though they themselves are not Metamei the clothes (of those deal with them), only food and drink ...

Proof (cont.): ... whereas according to the Rabanan, Parah and Parim are Metamei Tum'as Ochlin u'Mashkin, but not the Sa'ir ha'Mishtal'ach, since it is still alive.

Proof (cont.): And the Gemara asks that 'Rebbi Meir is easily understood, since he concurs with Tana de'bei Rebbi Yishmael, who learns 'If already seeds ... ' ...

Proof (cont.): ... but as far as the Rabanan is concerned, if they hold like Tana de'bei Rebbi Yishmael, then even the Sa'ir too (should be Metamei Tum'as Ochlin), whereas if they don't, then from where do they know Parah and Parim?

Conclusion: And the Gemara answers that it needs a Hechsher Tum'ah from another source - in other words, even though, since they stand to finally become a stringent Tum'ah, they do not require a Hechsher Tum'ah, they do require a Hechsher Ochel ...

Conclusion (cont.): Consequently, the Sa'ir ha'Mishtale'ach, which is not fit to eat whilst it is still alive, is not Metamei.

Triple Machlokes: And they argue as follows: Rebbi Meir holds that what it stands to become Tamei Tum'ah Chamurah is effective to render it a food, whereas according to the Rabanan only Parah and Parah are Metamei, but not the Sa'ir ha'Mishtale'ach, since it does not render it a food.

Rebbi Shimon: Rebbi Shimon, on the other hand, holds specifically Parah, because, since it had a Sha'as ha'Kosher, it falls under the category of 'food that one can feed to others', but not Parim and Sa'ir ha'Mishtale'ach, which did not have a Sha'as ha'Kosher ...

Proof #1: ... and this is evident in the Tosefta of Parah (at the end of the seventh Perek) - where, after citing the opinions of Rebbi Meir and the Rabanan, the Tana citing Rebbi Shimon, states that 'Parah is Metamei Tum'as Ochlin, since it had a Sha'as ha'Kosher, but Parim ha'Nisrafin and Se'irim ha'Nisrafin are not, since they did not have a Sha'as ha'Kosher'.

Proof #2: The Ri brings another proof from the fact that in many places, the Tana says 'They need Machshavah, but not Hechsher' ...

Example #1: In Perek Dam Shechitah (K'risus, Daf 21a) in connection with 'The Neveilah of a Beheimah Teme'ah everywhere, but that of a bird, only in the villages' ...

Example #2: In Perek Ba Si'man (Nidah, Daf 50b) in the case of 'A dove that fell into a vat'.

Example #3: And at the beginning of Taharos (1:1) in connection with 'the Neveilah of a Tahor bird' ...

Proof (cont.): In that, even though they do not require a Hechsher, since the stand to become Tamei Tum'ah Chamurah, they nevertheless require Machshavah ...

Proof (concl.): ... because to render them a food, the fact that it stands to become Tamei Tum'ah Chamurah is not effective.

Question #1: Does Rebbi Meir really argue in all these cases?

Question #2: Moreover, in Perek Gid ha'Nasheh (Chulin, Daf 102a) and in Perek T'vul-Yom (Zevachim, Daf 105b) the Gemara wants to prove that the ruling (in Maseches Taharos) that 'It (the Neveilah of a Tahor bird) needs Machshavah but not Hechsher' goes like Rebbi Meir, since the Seifa there - 'Shechitah u'Melikah Metaheres T'reifasah mi'Tum'asah', goes like him ...

Question #2 (cont.): ... and it refutes it on the grounds that "What has one to do with the other? the Seifa goes like Rebbi Meir and the Reisha, like the Rabanan!" '.

Question #2 (concl.): How could the the Gemara have even tried to establish it like Rebbi Meir, seeing as 'Tz'richah Machshavah' cannot go like him?

Question #3: Furthermore, in 'ha'Or ve'ha'Rotev' (Chulin, Daf 128b & 129a) in connection with 'Chatach Basar min Eiver min ha'Chai', the Tana writes 'Chatcho ve'Achar-kach Chishev alav, Tahor; Chishev alav ve'Achar-kach Chatcho, Tamei' , which it establishes like Rebbi Meir ...

Question #3 (cont.): ... and the Gemara there asks that according to those who establish the case by Huchshar, why that is necessary, seeing as it stands to become a Tum'ah Chamurah via its father (the body of the animal from which it was severed)? ...

Question #3 (concl.): ... implying that, even though the author is Rebbi Meir, there is no problem in saying that the fact that it stands to become a Tum'ah Chamurah via its father in that it does not require Hechsher, but not regarding Machshavah?

Answer: The Ri therefore explains that one can differentiate between the Sa'ir ha'Mishtale'ach, which, if it was not Shechted, would automatically be fit to eat if it were to be Shechted, without Machshavah, on the one hand ...

Answer (cont.): ... and the Neveilah of a Tahor bird and Eiver min ha'Chai, which do not stand to become a food, in which case Rebbi Meir will concede that it requires Machshavah, on the other.

Text #1: The text reads 'Parah Metamei', and not 'Parah Mitam'ah' ...

Reason: Because what difference will the fact that it becomes Tamei make? If it is inasmuch as it renders others Tamei - seeing as it had a Sha'as ha'Kosher, it has the status of a food, in which case it will render others Tamei even without receiving Tum'ah, seeing as it stands to become a Tum'ah Chamurah?

Support: And in the Tosefta too (at the end of Perek 7), it is evident that the correct text is 'Metamei', and not 'Mitam'ah', when it says 'Metamei Ochlin u'Mashkin'.

Text #2: If, on the other hand, the text does read 'Mitamei', we will have to explain it like Rashi - where one combined it with less than a k'Beitzah of dough, since the Parah cannot be Metamei the dough, since the fact that it stands to become a Tum'ah Chamurah will only be effective to the extent that it is as if it touched a Sheretz ...

Text #2 (cont.): ... and in this case, even if it touched a Sheretz it would not render the dough Tamei, seeing as the Basar of the Parah was less than a k'Beitzah.

Text #2 (concl.): And that explains why it requires Kabalas Tum'ah from another source, in order to render the dough Tamei.

Question: What difference does the fact that it combines with less than a k'Beitzah (of dough), seeing as in any event, even the smallest measure of food is subject to Tum'ah (mi'de'Rabanan)?

Possible Answer: ... and if it is to receive Tum'ah d'Oraysa - with regard to burning Kodshim on account of it, that is fine if we hold that Chibas ha'Kodesh of Parah is d'Oraysa, even though it has not been sanctified in a K'li ...

Question (cont.): ... but if it is only mi'de'Rabanan, then the foods in question will only be subject to Tum'ah mi'de'Rabanan, since min ha'Torah, it is as if it has been burned, and is considered like dust?

Another Tack: Furthermore the Ri explains, the fact that it receives Tum'ah from a Sheretz invalidates it - and if not for the fact that it had a Sha'as ha'Kosher, it would not receive Tum'ah and would not be Pasul ...

Implied Question: Because even though the Torah insists that those who deal with it must be Tahor, that is not because they will otherwise be Metamei it ...

Proof: .. but a Gezeiras ha'Kasuv, seeing as even if they were to handle it with a cane or with a flat wooden vessel, they would still have to be Tahor ...

Question: If it is to invalidate the Parah itself, also the ashes will be invalidated when they touch Tum'ah ...

Question (cont.): As the Gemara says in Perek Chomer ba'Kodesh (Chagigah 23a & 23b), when it prohibits carrying 'the ashes or the water of the Chatas' and transporting them on a boat, due to the incident that it relates there.

Answer: If it is considered a food, it will receive Tum'ah from a Sheini or a Shelishi, but not if it is not.

Refuted Answer #1: Nor can one explain that the difference it makes if it is Mitamei Tum'as Ochlin is that, since it has become Pasul and it is no longer subject to Tum'ah Chamurah, it still retains Tum'as Ochlin ...

Refuted Answer #2: Alternatively, what Rebbi Shimon means is that, if after it became Pasul it is touched by a Sheretz, it is Mitamei Tum'as Ochlin, seeing as it had a Sha'as ha'Kosher ...

Reason: ... because the fact that it was once Tamei Tum'ah Chamurah does not affect it ...

Reason (cont.): ... seeing as now it will no longer adopt a Tum'ah Chamurah - and proof of this lies in Perek Beheimah ha'Maksheh (Chulin, Daf 73b).

Conclusion: There is no point in dwelling further on this point, since there is absolutely no justification in explaining it like this ...

Proof: ... due to the Gemara's Kashya in Menachos (Daf 102b) 'Since "Whatever stands to be burned is considered as if it is already burned", why are Nosar and Parah Mitamei Tum'as Ochlin?' ...

Proof (cont.): What is the problem? Seeing as the Parah already received Tum'ah, now that it became Pasul, it no longer stands to be burned and retains the status of Maga Tum'ah?

Refuted Answer: And even if the Sheretz touched it only once ...

Refutation: Nevertheless, the moment the Parah makes contact, it becomes Pasul, and at the end of the contact it is Mitam'ah Tum'as Ochlin, since then it is no longer subject to burning.

Clarification: What the Gemara seems to be saying is that it is permitted to redeem it, even mi'de'Rabanan ...

Proof: ... since at the end of the first Perek of Shevu'os (Daf 11b), on the Beraisa (Tosefta, Maseches Parah 2:2) 'Shachtah al-Gabei Ma'arechtah, Ein lah Pediyah Olamis'.

Proof (cont.): ... the Gemara extrapolates that it does not go like Rebbi Shimon, according to whom it can be redeemed, as we see here.

Question: When the Rabanan say that it cannot be redeemed, that cannot be min ha'Torah ...

Reason: Seeing as it is subject to Ha'amadah ve'Ha'arachah as long as it is still Mefarcheses - according to one of the explanations cited above (on Daf 76a, DH Shechitah) ...

Reason (cont.): ... In that case, how does Resh Lakish know that Rebbi Shimon argues with the Rabanan? Perhaps he concedes that it is not subject to Pediyah mi'de'Rabanan, only mi'd'Oraysa, and it is Mitanei Tum'as Ochlin, since it had a Sha'as ha'Kosher?

Refuted Answer: It is a Dochek to say that even though min ha'Torah it had a Sha'as ha'Kosher, seeing as mi'de'Rabanan it is not subject to Pediyah, it is not considered food that one can feed to others.

Answer: The one who forbids, forbids even mi'd'Oraysa, seeing as he Shechted it li'Shemah for the Hechsher of the Korban, whilst the one who permits, permits even mi'de'Rabanan, until the Kohen has performed the Haza'os, as Tosfos explained earlier (on Amud Alef, DH 'Parah' 1).

Refuted Reason: If, according to the Rabanan, Parah would be Kodshei Mizbe'ach, it would be understood (why it is Asur mi'd'Oraysa).

Refutation: However it is not feasible that any Tana considers Parah Kodshei Mizbe'ach ...

Proof #1: ... since the Gemara, at the beginning of 'Ein Ma'amidin' (Avodah-Zarah, Daf 23b & 24a) asks in surprise 'Does this mean that Parah is Kodshei Mizbe'ach'?

Proof #2: Moreover, in many places in Shas the Gemara says that 'the Torah calls it a Chatas' - implying that intrinsically, it is Kodshei Bedek ha'Bayis ...

Implied Question: And even though the Mishnah in Shekalim (4:6) states that it is purchased from T'rumas ha'Lishkah' ...

Answer: ... that is because, since it is the Kohanim who bring the Korbanos who need it, it is considered for the needs of Korbanos, and 'the heart of Beis-Din' makes the necessary stipulation) ....

Precedent: ... bearing in mind that even those who teach the Kohanim the Dinim of Kemitzah take their remuneration from the T'rumas ha'Lishkah ...

Answer (cont.): And even without 'the heart of Beis-Din stipulating' on the contents of the Lishkah, it may well be that one may use it for these things min ha'Torah, seeing as they are for the needs of the Korbanos.

Clarification: Consequently, when we say that it is Kodshei Bedek ha'Bayis ...

Clarification (cont.): That is not to say that it is purchased from Kodshei Bedek ha'Bayis funds ...

Clarification (concl.): ... but that it has the Din of Kodshei Bedek ha'Bayis, that its Kedushah is that of Kedushas Damim, and not Kedushas ha'Guf, like Kodshei Mizbe'ach (See Hagahos ve'Tziyunim).

Question: And Mocher on Shabbos, which is Chayav, even though Tavach is not ...

Answer: ... since that animal is subject to Tevichah on a weekday ... .

Introduction to Question: In Perek Oso ve'es B'no (Chulin, Daf 78b & 79a), Rashi explains that Rava learns the Binyan Av from the Pasuk "Shor Seh Kesavim ve'Seh Izim".

Question: The Ri queries this however, since later (on Daf 78a) the Gemara explains that Rava goes according to Rebbi Eliezer (See Hagahos ve'ha'Tziyunim), with regard to a Tamei animal that is born from a Tahor animal that conceived from a Tamei one, and not like Rebbi Yehoshua ...

Question (ont.): ... who has no need of Rava's Binyav Av, seeing as he learns it from "Seh Kesavim" and from "Seh Izim".

Question (concl.): On the contrary (according to Rashi) Rava's Binyan Av is from that same Pasuk?

Answer: The Ri therefore explains that Rava learns the Binyan Av from "Seh" of Pesach, by which the Torah writes (in Sh'mos 12) "Seh Tamim Zachar ben Shanah Yih'yeh lachem min ha'Kevasim u'min ha'Izim Tikachu".

Proof: And to prove this, the Gemara concludes (on Daf 78a) that Rava is speaking in connection with Petter Chamor, as we learned in the Mishnah "Ein Podin ... ' ...

Proof (cont.): ... and at the end of the first Perek of Bechoros (Daf 12a & 12b) the Gemara learns that from a Gezeirah-Shavah "Seh" "Seh" from Pesach.

Question #1: Why does the Gemara here refer to it as a 'Binyan Av', and in Bechoros as a 'Gezeirah-Shavah' - by virtue of the statement 'It says here "Seh" and it says further on "Seh" '.

Question #2: Why does Rava mention 'Kil'ayim' more than 'a calf', 'a Chayah', 'a T'reifah' and a 'Shechutah', all of which, we learn from "Seh" of Pesach, cannot be used to redeem a Petter Chamor ...

Source: ... seeing the Gemara says there 'Just as there, it excludes all of these cases'?

Question #3: Why does it not ask here 'T'reifah! - But the Torah writes "Seh"?', like it asks with regards to Kil'ayim?

Question #4: Furthermore, why does Rebbi Eliezer, who allows redeeming a Petter Chamor with Kil'ayim, not also permit redeeming it with a Shechutah and a T'reifah, since he establishes the Binyan Av by a Tamei animal that is born from a Tahor one ... ?

Question #5: Moreover, when the Gemara asks later according to Rebbi Eliezer what the Binyan Av of Rava comes to teach us, why does it not answer that it comes to preclude the other types of animals (besides Petter Chamor), with which one cannot redeem it?

Refuted Answer: And if you will say that we learn a T'reifah and a Shechutah from the implication of the word "Seh", like a calf and and a Chayah ...

Refutation: ... but the Gemara says in Perek Hotzi'u lo (Yoma, Daf 49b Tosfos DH 'Sha'ani') that even a Shechted bull is called "Par" ...

Refutation (cont.): ... and the same would apply to "Seh" of Pesach, had the Torah not written 'mi'Heyos Mi'Seh", from which the Chachamim extrapolate 'mi'Chiyuteih de'Seh' (only as long as it is alive).

Answer: The Ri therefore explains that Rava's Binyan Av and the Gezeirah-Shavah in Bechoros are not one and the same ...

Answer (cont.): ... because even though both are learned from "Seh" of Pesach, Rava learns the Binyan Av from the extra words 'min ha'Kevasim u'min ha'Izim Tikachu" - which implies that the father must be a 'Keves' and the mother, a 'Kivsah'.

Answer (cont.): This Limud is not needed for itself, seeing as we can learn it from other Kodshim ...

Source: ... as the Beraisa will shortly say "Shor O Kesev O Eiz" - 'to preclude Kil'ayim' ...

Answer (cont.): ... but to learn from it the principle 'Wherever the Torah writes "Seh", it comes specifically to preclude Kil'ayim'.

Implied Question: ... and if not for the Binyan Av, we would not have precluded Kil'ayim from the Gezeirah-Shavah of "Seh" "Seh" ...

Answer: ... because we would have then said that "Tifdeh Tipadeh" includes it ...

Precedent: ... in the same way as we do not preclude there whatever is not a Zachar, Tamim or ben Shanah from the Gezeirah-Shavah, because "Tifdeh Tipadeh" includes it.

Implied Question: And it is a S'vara to preclude them all from the Gezeirah-Shavah of "Seh" more than Kil'ayim ...

Answer: ... since Kil'ayim is also called "Seh".

Conclusion: And that explains why Rebbi Eliezer establishes Rava's Binyam Av by a Tamei that is born ... ' (permitting Kil'ayim).

Introduction to Question: Later (on Daf 78a), when the Gemara says 'If it comes for Kodshim, the Torah specifically precludes Kil'ayim by them' - implying that had it not done so, we would have indeed learned it from "Seh" of Pesach (from the Binyan Av) ...

Implied Question: Even though the basic Binyan Av by Pesach is only superfluous because it is not needed for itself, since we learn it from Kodshim ...

Answer: ... such is the way of the Gemara, to make out as if it knows certain facts from another source ...

Answer (cont.): And what the Gemara means is - 'If it comes for Kodshim, and you will say that we learn from another Pasuk to preclude Kil'ayim on Pesach ... '.

Precedent: And we find a similar set-up at the beginning of Kidushin (Daf 3b Tosfos, DH 've'Chi') and in Perek Na'arah (Kesuvos, Daf 46b) in connection with 'Kidushei ha'Bas le'Avihah' - where the Gemara says 'And if you say let us learn it from Boshes and P'gam' ...

Precedent (cont.): ... even though we only know that Boshes and P'gam themselves go to the father from Kidushin, as the Gemara explains at the end of 'Eilu Na'aros' (Ibid, Daf 40b, Tosfos DH 'de'I').

Question: Without this, the Gemara could have said that, in connection with Geneivah, the Torah writes "Seh" to preclude Kil'ayim, like Rava, the Torah therefore writes "O" to include it?

Answer: Rava's statement is confined to where the Torah writes only "Seh" . whereas here it writes "Shor" as well.