1)

(a)We just learned the principle of 'Aseh Docheh Lo Sa'aseh' from the Semuchim "Lo Silbash Sha'atnez ... Gedilim Ta'aseh Lach". But that Derashah is learned by Tana d'Bei Rebbi Yishmael exclusively. The Rabanan disagree with it - because, according to them, the Pasuk needs to write "Tzemer u'Fishtim", (seeing as "Begadim" per se does not necessarily mean wool or linen). Consequently, it is not Mufneh.

2)

(a)The Torah having written in Kedoshim "Lo Sakifu Pe'as Roshchem", we learn from the word "Rosho" (in the Pasuk in Metzora [in connection with the Metzora's purification ceremony] "Yegalach es Kol Se'aro, es Rosho") - that the Mitzvah of a Metzora shaving off all the hair of his head overrides the Lav of "Lo Sakifu ... ".

(b)This Tana must hold 'Hakafas Kol ha'Rosh Shemah Hakafah' - because, if he did not, then he would not require a Pasuk to permit shaving the hair of a Metzora, seeing as by shaving off all his hair (which the Torah requires), he does not contravene the Lav of "Lo Sakifu" anyway.

(c)We reject this as the source for 'Aseh Docheh Lo Sa'aseh' - because the Lav that is being overridden ("Lo Sakifu") is a Lav that does not pertain to everyone (i.e. women are Patur, as the Gemara explains in Kidushin), so we could learn not from it Lavin that apply to everybody.

(d)We know that the woman too, is Chayav for transgressing the Lav of Achos Ishah - because of the Pasuk in Acharei-Mos "v'Nichr'su ha'Nefashos ha'Osos", which by virtue of the plural form, implies that the woman who is guilty of incest is Chayav no less than the man.

3)

(a)So we try to learn 'Aseh Docheh lo Sa'aseh' from 've'es Zekano (in the same context). The Torah writes "u'Pe'as Zekanam Lo Yegalechu" - by Kohanim.

(b)We try to learn from "v'es Zekano" - that the obligation of a Kohen who is a Metzora to shave off his beard, overrides the Lav of "u'Pe'as Zekanam Lo Yegalechu" (a proof that 'Aseh Docheh Lo Sa'aseh').

(c)in spite of having just rejected the proof from the Lav of "Lo Sakifu ..." because it is a Lav she'Eino Shaveh ba'Kol - we nevertheless think that that this proof is acceptable (despite the fact that this Lav too, is also a Lav she'Eino Shaveh ba'Kol) - because since we do not require two sources to teach us 'Aseh Docheh Lav she'Eino Shaveh ba'Kol', we apply the second Pasuk (via 'Im Eino Inyan') to a 'Lav ha'Shaveh ba'Kol'.

(d)We refute this proof too however - on the grounds that Kohanim are different (because they have many extra Mitzvos), and we therefore need this Pasuk to teach us 'Aseh Docheh Lo Sa'aseh she'Eino Shaveh ba'Kol by Yisraelim (but not Lo Sa'aseh ha'Shaveh ba'Kol').

4)

(a)So we cite the Beraisa which says that "Rosho" of Metzora overrides the Lo Sa'aseh of Nazir "Ta'ar Lo Yavo Al Rosho". But we reject too, as a source for 'Aseh Docheh Lo Sa'aseh' - on the grounds that the Lav of a Nazir is less stringent than other Lavin, because it is possible to have one's Nezirus (together with any Mitzvos attached to it), nullified.

(b)We prove this refutation - on the grounds that, if this was a genuine source for 'Aseh Docheh Lo Sa'aseh', then we ought to go further and learn from here that an Aseh can even override a Lav together with an Aseh (because a Nazir has the additional Aseh of "k'Chol ha'Yotzei mi'Piv Ya'aseh"), yet we have a principle 'Ein Aseh Docheh Lo Sa'aseh va'Aseh'.

5)

(a)So we revert to our original source, to learn 'Aseh Docheh Lo Sa'aseh' (even according to the Rabanan of Tana d'Bei Rebbi Yishmael) from the Semuchim of "Lo Silbash Sha'atnez ... Gedilim Ta'aseh Lecha". We first try to learn it from the word "Gedilim" - and what makes "Gedilim" Mufneh is that the Torah could have written "Tzitzis".

(b)We reject this however, on the grounds that "Gedilim" is not superfluous, because it is needed - to teach us that Tzitzis comprises four threads (because 'Gedil' implies a minimum of two, and 'Gedilim' turns this into four - part Gedil and part Pesil [which we learn from "Tzitzis"] - see Menachos 39b. Rashi there and Shitah Mekubetzes. See also Tosfos here DH 'Gedilim').

(c)"Yachdav" too, is not Mufneh - because we learn from it that the two materials must be properly joined (sewn with at least two stitches), in order to be Chayav.

(d)We initially reject the suggestion that the word "Sha'atnez" is Mufneh - because we need it to Darshen 'Shu'a Tavuy and Nuz' (which we will now explain.

6)

(a)The meaning of ...

1. ... Shu'a is - smooth (i.e. combed together - see Tosfos DH 'Ad', regarding all three terms).

2. ... Tavuy is - spun.

3. ... Nuz is - woven.

(b)We ultimately conclude that "Sha'atnez" is Mufneh after all - because otherwise, the Torah should have written "Shu'a, Tavuy v'Nuz", instead of the shortened version of "Sha'atnez".

7)

(a)We now need to prove that 'Aseh Docheh Lo Sa'aseh' even by a Lav she'Yesh Bo Kares (in order that "Alehah" should be required to preclude Achos Ishto from the Mitzvah of Yibum). Despite the fact that it overrides Shabbos, we cannot learn any other Aseh from ...

1. ... Bris Milah - which is special inasmuch as Hash-m made thirteen Brisos with Yisrael on its account.

2. ... Korban Pesach - because it carries with it a Chiyuv Kares.

3. ... Korban Tamid - which is a regular (daily) Mitzvah.

(b)Neither can we learn it from a combination of ...

1. ... Pesach and Milah - because both of them carry a Chiyuv Kares.

2. ... Pesach and Tamid - both of which are Tzorech Gavo'ah (for the needs of Hash-m [kiv'Yachol] as opposed to Yibum, which is for the needs of the Yavam and the Yevamah).

3. ... Milah and Tamid - since they were both practiced already before Matan Torah.

(c)The Tana who learns that the Olah that they brought at Har Sinai was not the Olas Tamid might indeed learn 'Aseh Docheh Lo Sa'aseh she'Yesh Bo Kares' from these two. According to him, the Olah that they brought at Har Sinai - was an Olas Re'iyah.

(d)We cannot learn 'Aseh Docheh Lo Sa'aseh she'Yesh Bo Kares' from all three, Milah, Pesach and Tamid - because Pesach too, was already practiced before Matan Torah.

8)

(a)We learn from the Pasuk in Kedoshim "Ish Imo v'Aviv Tira'u, v'es Shabsosai Tishmoru, Ani Hash-m" - that, seeing as parents are no less obligated to obey Hash-m than their children, they have no authority to order their children to break Shabbos (or anything else that contravenes Hash-m's word for that matter).

(b)We try to learn from there that 'Aseh Docheh Lo Sa'aseh she'Yesh Bo Kares' - by inferring that, were it not for "Ani Hash-m", a person would indeed, it seems, be obligated to obey his parents and break Shabbos, which is a 'Lav she'Yesh bo Kares'.

(c)We refute this Limud however - by establishing Shabbos to mean the Lav of Mechamer (driving one's donkey, for which there is no Kares) exclusively.