Answer (Rav Ashi): The Torah taught that Heter joins to Isur in two places - Isurei Nazir and absorptions of a Korban Chatas;

Whenever there are Shenei Kesuvim ha'Ba'im k'Echad (two verses that teach the same principle, and one of them could have been learned from the other), we do not learn from them to other cases.

The case of Nazir is as above; absorptions of a Chatas are as follows:

(Beraisa) Suggestion: "Kol Asher Yiga bi'Vsarah Yikdash" (any food that touches a Chatas becomes Kodesh) - perhaps this is even if the food did not absorb!

Rejection: "Bi'Vsarah" - it is Kodesh only if Chatas is [absorbed] in the meat.

"Yikdash" - the food it touched become like the Chatas - if the Chatas is Pasul [and may not be eaten], the food may not be eaten; if the Chatas is Kosher, the food may be eaten with the stringencies of Chatas (male Kohanim may eat it in the Azarah until dawn. Stringencies of the other food, e.g. if it was a Shelamim offered yesterday which may be eaten only until nightfall tonight, also apply.)

Question: Chachamim should agree that these are Shenei Kesuvim [ha'Ba'im k'Echad - why do they learn Ta'am k'Ikar from Nazir to all Isurim]?!

Answer: They say that these are not Shenei Kesuvim because we could not learn either from the other.

R. Akiva holds that one is extra:

Granted, we could not learn Nazir from Chatas - we do not learn [stringencies] from Kodshim to Chulin;

But we could learn Chatas from Nazir - we could learn from Nazir to the entire Torah!

Chachamim say that both are needed - Chatas is needed to teach that Heter joins to Isur; this does not apply to Chulin, because we cannot learn Chulin from Kodshim;

Mishras is needed to teach that Ta'am k'Ikar - we learn to all Isurim.

R. Akiva holds that both teach that Heter joins to Isur, therefore they are Shenei Kesuvim, and we may not learn from them.

Question (Rav Ashi - Beraisa): "Mi'Kol Asher Ye'aseh mi'Gefen ha'Yayin me'Chartzanim v'Ad Zag" - this teaches that all Isurim [of vine products] of Nazir join with each other.

R. Akiva holds that Heter joins to Isur - there is no need to teach that Isur joins to Isur!

Answer (Rav Kahana): Heter joins to Isur only if they are eaten together, but Isur joins to Isur even if they are eaten one after the other.

(Mishnah): If dough is in cracks in a kneading trough:

If there is a k'Zayis in one place, he must destroy it;

If not, it is Batel because it is so small. (This Bitul is not standard Bitul Chametz - rather, since it is unimportant, it is considered like part of the trough.)

The same applies to Tum'ah - if one is Makpid about it (intends to remove it), it is a Chatzitzah; if he wants it to stay there, it is like part of the trough (this will be explained).

Version #1 (Gemara - Rav Yehudah): This (the obligation to destroy a k'Zayis in one place) is only in a place where it does not strengthen [the trough] - but in a place where it strengthens it, one need not destroy it (one will surely leave it there, it is Batel to the trough).

Inference: This implies that one need not destroy less than k'Zayis even in a place where it does not strengthen it.

Version #2 - (Mishnah): If not, it is Batel because it is so small.

(Rav Yehudah): This is only in a place where it strengthens it - but in a place where it does not strengthen it, one must destroy it.

Inference: This implies that one must destroy a k'Zayis even in a place where it strengthens it.

Support (for Version #1 - Beraisa #1): If dough is in cracks in a kneading trough:

In a place where it strengthens it, it is not a Chatzitzah, and one does not transgress [Bal Yera'eh and Bal Yimatzei on account of it];

In a place where it does not strengthen it, it is a Chatzitzah, and one transgresses.

This refers to a k'Zayis - but less than k'Zayis is not a Chatzitzah, and one does not transgress, even in a place where it does not strengthen it.

Support (for Version #2, and Contradiction - Beraisa #2): If dough is in cracks in a kneading trough:

In a place where it strengthens it, it is not a Chatzitzah, and one does not transgress;

In a place where it does not strengthen it, it is a Chatzitzah, and one transgresses.

This refers to less than a k'Zayis - but a k'Zayis is a Chatzitzah, and one transgresses, even in a place where it strengthens it.

Resolution #1 (Rav Huna): The lenient [Beraisa, i.e. #1, is erroneous; it] must be deleted on account of the stringent (Beraisa #2 is correct).

Resolution #2 (Rav Yosef): [Both are correct -] Tana'im argue about this!

(Beraisa): One must destroy moldy bread, because one can grind it up and use it to ferment other dough (therefore, it is forbidden like Se'or);

R. Shimon ben Elazar says, this is if it is being kept [for fermenting, which is] for the sake of eating - but Kofes Se'or (a block of heavily leavened dough) which was designated for sitting is Batel.

Inference: Only R. Shimon says that it is Batel - the first Tana holds that even 'Bitul' (designation for sitting) does not help for a k'Zayis [it is still considered Chametz]!

Objection (Abaye): You explain the argument about a k'Zayis - how do you explain the argument about less than k'Zayis? (Even R. Shimon would not say that it is Batel in a place where it does not strengthen it, for it is standing to be eaten!)

Resolution #3 (Abaye): Beraisa #1 and Beraisa #2 are both like R. Shimon [they do not argue, just they use the same words to refer to different places]:

Beraisa #1 discusses only where kneading is done (the bottom and walls, but not the rim) - it calls the bottom a place where it strengthens (even a k'Zayis is Batel, for it is urgently needed to hold water which gathers there), and it calls the walls a place where it does not strengthen (less than a k'Zayis is Batel, but a full k'Zayis is not Batel, for the walls need not be so watertight);

Beraisa #2 discusses even where kneading is not done (the rim) - it calls the walls a place where it strengthens (less than a k'Zayis is Batel), and it calls the rim a place where it does not strengthen (no amount is Batel).

(Rav Ashi): Do not think that 'Where kneading is not done' only refers to the back [outside] of the rim [but on top of the rim is considered a place of kneading] - rather, 'Where kneading is not done' refers [even] to on top of the rim.

Objection: This is obvious (people do not knead on top)!

Answer: One might have thought that since sometimes the dough swells and covers the rim, it is considered a place of kneading - Rav Ashi teaches that this is not so.

Version #1 (Rav Nachman citing Rav): The Halachah follows R. Shimon.

Question: But Rav Yitzchak bar Ashi said in the name of Rav that if one plastered Kofes Se'or [to sit on it], it is Batel!

Answer: Amora'im argue about the opinion of Rav.

Version #2 (Rav Nachman citing Rav): The Halachah does not follow R. Shimon, for Rav Yitzchak bar Ashi said in the name of Rav that if one smeared the outside of the dough with mud, it is Batel. (end of Version #2)

(Rav Nachman): If two half k'Zeisim [of Chametz] are joined by a strip of dough:

If when one picks up the strip the Chametz comes with it, one must destroy them; if not, not.

(Ula): This applies only to a kneading trough - but in the house, [in either case] he must destroy them.

Question: What is the reason?

Answer: He might [sweep the house and] bring them together.

Questions (Chachamim of Eretz Yisrael): Do the half k'Zeisim join if one is in the house and the other is in one of the following places:

The upper story; an Achsadra (a room open on one side); another house interior to the first?

These questions are not resolved.

(Beraisa): If bread became moldy and is not fit for people to eat but dogs can eat it, it has Tum'as Ochlim if it is k'Beitzah (the size of an egg), and [even if it is Terumah] it may be burned with Tamei [Chametz] on [Erev] Pesach;

R. Noson says, it does not have Tum'as Ochlim.

Question: Who is the Tana of the following Mishnah?

(Mishnah): The general rule is - anything [that was initially] fit for people to eat is Mekabel Tum'ah as long as dogs can eat it.

Answer: It is unlike R. Noson.

(Beraisa): If flour was put in a tanning bowl:

If it was put within three days of Pesach, one must destroy it; if it was more than three days before Pesach, he need not destroy it (the smell of the Keli spoils it - excrement is used in tanning).

R. Noson says, this is if it was not put with hides - but if it was put with hides, in either case he need not destroy it.

(Rava): The Halachah follows R. Noson, even if it was put the same day [Erev Pesach], even a short time [before Bi'ur].

(Mishnah): The same applies to Tum'ah - if one is Makpid about it, it is a Chatzitzah; if he wants it to stay there, it is like part of the trough.

Question: This is not 'the same' - Bi'ur depends on a Shi'ur, Tum'ah depends on Kepeidah!

Answer #1 (Rav Yehudah): Indeed, it means 'But Tum'ah is different...'

Objection (Abaye): The Mishnah says 'The same applies to Tum'ah'!