1) PROOF FOR THE CONCEPT OF "DAYO" FROM MIRIAM'S ISOLATION PERIOD
OPINIONS: The Gemara proves the concept of "Dayo la'Ba Min ha'Din Liyehos ka'Nidon" -- it is sufficient to give the Halachah learned from a Kal va'Chomer the exact status of the Halachah from which it was learned (and not a more stringent Halachah) -- from the incident of Miriam's isolation. The verse teaches a logical reason, based on a Kal va'Chomer, for why Miriam was sent out of the encampment of the Jewish people for seven days: "v'Aviha Yarok Yarak b'Faneha ha'Lo Sikalem Shiv'as Yamim" -- "If her father would have rejected her, would she have not been scorned (and isolated) for seven days" (Bamidbar 12:14), then certainly when Miriam was rejected by the Shechinah she should be isolated for seven days (but not for fourteen days, because of the rule of "Dayo"). (See Insights to Bava Kama 25:1 for the source of the Halachah that one who is shunned by his father is isolated for seven days.)
The Gemara clearly implies that because Miriam sinned against Hash-m, she should have been sent away for double the time. The Torah teaches that "Dayo" limits the Halachah that is derived through the Kal va'Chomer to the degree of severity of the Halachah's source.
What is the basis for the Gemara's assumption that the punishment for one who sinned against Hash-m should be double that of one who sinned against a parent?
(a) TOSFOS (DH Kal va'Chomer) quotes RABEINU TAM who explains the Gemara's assumption based on the Gemara in Nidah (31a) which teaches that there are three partners in the creation of a person: Hash-m, the father, and the mother. Hash-m's portion in the creation of a person is equal to the portion of the father and mother together. That is, there are four portions in the creation of a person -- two which are contributed by Hash-m, and one by the father and one by the mother. It follows logically that if a person who sins against his father -- who contributed "one part out of four" to his creation -- is shunned for seven days, then one who sins against Hash-m -- Who contributed "two parts out of four" -- must be shunned for twice that amount, or fourteen days.
Tosfos, however, is not satisfied with this answer. Tosfos asks that according to this answer, even without a Kal va'Chomer it would be known that one who sins against Hash-m should be shunned for fourteen days. Moreover, the Sifri states that the reason why Miriam should have been punished for fourteen days was that she spoke Lashon ha'Ra about Moshe Rabeinu, who had the status of a king and a Kohen Gadol (as he served in the Mishkan during the seven inaugural days). The Sifri seems to contradict Rabeinu Tam's logic regarding the source for fourteen days. (See RASHASH, who understands that this question is also the intent of Tosfos, unlike the MAHARSHA understands it.) Tosfos suggests that it is possible to explain that according to Rabeinu Tam, when the Sifri mentions that Miriam sinned against the "Melech," it refers not to Moshe Rabeinu but to Hash-m. However, Tosfos rejects this approach since it is not consistent with the wording of the Sifri.
(b) Tosfos quotes RABEINU CHAIM who explains that the verse does not mean that one who sins against Hash-m should be punished for fourteen days, but rather for a little more than seven days. Once the verse says that the period of punishment should be more than "Hisager" -- "she should be shut out" (Bamidbar 12:14), it adds another period of "Tisager" -- "she should be shut out" -- to show that Miriam deserved more punishment than just one period of isolation. This indicates fourteen days.
The RAN gives a similar explanation. Once the Torah teaches that Miriam deserved more than seven days, and the Halachos of a Metzora teach that the Metzora is shunned in seven-day increments, "more than seven" automatically means fourteen days. (Y. Montrose)

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2) HALACHAH: "SHTAR CHATZI ZACHAR" -- THE WAY IN WHICH A WIFE MAY INHERIT HER HUSBAND
QUESTION: The Gemara derives from the verse, "She'eiro" -- "his relative" (Bamidbar 27:11), that a husband inherits his wife's property when she dies. The verse adds, "v'Yarash Osah" -- "and he will inherit her," to teach that one should not think that a woman inherits her husband's property just as he inherits her property. Rather, he inherits from her, but she does not inherit from him.
If a man wants his wife to inherit part of his estate after his death, is there a Halachic way to set up such an inheritance?
ANSWER: The Poskim discuss various ways in which such a will may be established. One such way is called a "Shtar Chatzi Zachar," a "document of half of a male."
There are many variations of a "Shtar Chatzi Zachar." The basic formulation of such a document (see NESIVOS HA'MISHPAT CM 281:9) is that the man writes in his will (and makes a Kinyan to the effect) that he owes his wife (or daughter), whom he would like to receive a portion of his inheritance, a very large sum of money. He writes that this debt takes effect an instant before his death. He adds, however, a condition to this gift. If the other heirs will give his wife a sum of money equal to half of the share of an ordinary son of his who inherits his estate, his obligation to give her a large sum of money will become null and void.
This procedure has several advantages over merely giving a present to his wife during his lifetime which takes effect the moment before his death. One particular advantage is that if the man is uncertain about how much his estate will be worth when he dies, the "Shtar Chatzi Zachar" ensures that his wife will receive a fair share, and he does not have to guess at a sum of money which may be too large or too small.
HALACHAH: The writing of such a Shtar is deemed proper and acceptable according to Ashkenazic custom. (See REMA CM 281:7.) It was set up primarily so that a daughter would also receive a portion of her father's estate, but is also used for a wife. This legal procedure should be conducted only in consultation with a Rav and a legal expert familiar with the process, and who can ascertain that the document is written in a way that is Halachically and legally valid.
However, it seems that Sephardic custom does not accept this practice, and thus a Sephardic Jew should consult a competent Halachic authority with regard to the proper procedure. (Y. Montrose)