Question: Tana d'Vei R. Yishmael learns from Tzitzis that Aseh Docheh Lo Sa'aseh. What is Chachamim's source?

Answer #1: They learn from Taharas Metzora. He must shave (all his hair, including) his head (and transgress cutting the Pe'os):

(Beraisa): "Rosho" - if not for this verse, one would think that "Al Takifu Pe'as Roshchem" applies even to Taharas Metzora.

The Tana holds that one who cuts all the hair on his head transgresses cutting the Pe'os.

Objection: The Lav not to cut the Pe'os applies only to men. We cannot learn from here that an Aseh overrides a Lav that is Shavah b'Chol (applies to everyone)!

Answer #2: We learn from the Taharah of a Kohen Metzora. (Even though there is a special Mitzvah for Kohanim not to shave,) he shaves his beard.

(Beraisa): If not for "Zekano", one would have thought that "They (Kohanim) will not shave the corners of their beards" applies even to a Kohen Metzora. (Also Yisre'elim are commanded. The rejection of this answer is based on the Isur for Kohanim.)

Since we already learned that an Aseh overrides a Lav that is not Shavah b'Chol, this must teach that even a Lav ha'Shavah b'Chol may be overridden.

Objection: We need the verse to permit a Kohen Metzora to shave!

One might have thought that since the Torah gave extra Mitzvos to Kohanim, their extra Mitzvos are not overridden, even though they are not Shavah b'Chol!

Answer #3: We learn from "Rosho" like the following Tana:

(Beraisa) Suggestion: Perhaps "A razor will not pass over Rosho" applies to a Nazir even if he is a Metzora!

Rejection: "Rosho" teaches that the Mitzvah for a Metzora to shave overrides the Lav for a Nazir to shave (his head).

Since we already learned that an Aseh overrides a Lav that is not Shavah b'Chol, this must teach that even a Lav ha'Shavah b'Chol may be overridden.

Objection: The Isurim of a Nazir are weaker, since one can annul the Nezirus. We cannot learn to a regular Lav!

Support (for objection) Question: We hold that an Aseh does not override a Lav and an Aseh. Why don't we learn from Nazir that it does? (He also has an Aseh to grow his hair, "Kadosh Yihyeh Gadel Pera".)

Answer: We cannot learn from Isurei Nazir, since they can be annulled.

For the same reason we cannot learn from Nazir that an Aseh overrides a Lav.

Answer #4: Really, we learn from the Semichus of the Mitzvah of Tzitzis to the Isur of Sha'atnez.

It says "Gedilim" instead of 'Tzitzis' to teach that we should expound the Semichus.

Objection: It needs to say "Gedilim" to teach the number of threads!

'Gedil' is (strings wrapped together, i.e. at least) two. "Gedilim" (plural) is four;

Version #1 (Rashi): (These are inserted through the corner, making eight ends;) we make a Gedil (wrap them together). "Pesil" teaches that we leave part like Pesilim (unwrapped).

Version #2 (Tosfos): "Pesil" teaches that we (insert them through the corner and) fold them. (end of Version #2)

Answer #1: It would have sufficed to say "Sha'atnez Tzemer u'Pishtim". The Torah added "Yachdav " (together) to be free (to expound the Semichus).

Objection: We need this ("Yachdav") to teach that two stitches are considered connected, but one stitch is not!

Answer #2: The Torah could have said just "Tzemer u'Pishtim Yachdav ". "Sha'atnez" was added to be free.

Objection: We need the word "Sha'atnez" to teach that it must be Shu'A, Tavuy, and NuZ (smoothed, spun and woven)!

Answer: We learn everything from the word "Sha'atnez" (the Torah could have said 'Kil'ayim', and it could have explicitly said Shu'a, Tavuy, and Nuz).

Question: This shows that a regular Lav may be overridden. We still have not answered Question 5:d (Daf 3b), where do we find that a Lav with Kares is overridden (necessitating "Aleha" to teach that Yibum does not override Eshes Ach? Circumcision, Korban Pesach and the Tamid override Shabbos, but we cannot learn from them!)

We cannot learn from Milah, for 13 covenants were made over it!

We cannot learn from Korban Pesach, for one who neglects to offer it gets Kares!

We cannot learn from the Tamid, since this is a constant Mitzvah!

Suggestion: We cannot learn from any one of these. Perhaps we can learn from a Tzad ha'Shavah of two of them.

Rejection: We cannot learn from circumcision and Pesach, for both of these have Kares (but a regular Aseh does not override Kares);

We cannot learn from Pesach and Tamid, for these are needs of (Avodas Mizbe'ach of) Hash-m!

We cannot learn from circumcision and Tamid, for both of these preceded Matan Torah!

This is like the opinion that the Olos offered in the Midbar were Temidim.

We cannot learn from all three, since they all preceded Matan Torah!

Answer #1 (to Question #1, Sof Daf 3b): Had the Torah not written "Aleha" we would gave learned from Kibud Av va'Em that even a Mitzvah with Kares is overridden.

(Beraisa) Suggestion: Perhaps Kibud Av va'Em overrides Shabbos!

Rejection: "A man will fear his parents, and keep My Shabbosos" - all of you (even your parents) must honor Hash-m!

Suggestion: The parent told the child to slaughter or cook. If not for the verse, this would override a Melachah of Shabbos (which is Chayavei Kerisos)!

Rejection: No, he told the child to be Mechamer (make an animal work). This is a Lav (without Kares), yet it does not override Shabbos.