1) KIDNAPPING AND SELLING A PERSON
QUESTION: The Gemara discusses an argument between Chizkiyah and Rebbi Yochanan in the case of one who kidnaps and sells his victim. When two witnesses saw the kidnapping and two other witnesses saw the sale, Chizkiyah maintains that neither set can be made into Edim Zomemim. Rebbi Yochanan maintains that both sets can be made into Edim Zomemim.
The Gemara explains that this argument is based on an argument between Rebbi Akiva and the Chachamim. Chizkiyah follows the view of Rebbi Akiva who derives from the word "Davar" (Devarim 19:15) that the testimony of witnesses is valid only when all of the testimony is given by one set of witnesses, and it is not split up among numerous sets of witnesses -- "'Davar' v'Lo Chatzi Davar." When one set of witnesses testifies about the kidnapping and another set testifies about the sale, none of the testimony is acceptable. The Chachamim disagree and maintain that the testimony of each set of witnesses is valid because the two sets combine to form one complete "Davar," and Rebbi Yochanan follows their opinion.
If the basis of the argument between Chizkiyah and Rebbi Yochanan is the argument between Rebbi Akiva and the Chachamim concerning "Davar v'Lo Chatzi Davar," then why do Chizkiyah and Rebbi Yochanan discuss whether or not the witnesses can become Edim Zomemim? They should argue about whether or not the testimony of these witnesses is accepted in Beis Din in the first place to convict the defendant! (BA'AL HA'ME'OR)
ANSWERS:
(a) The BA'AL HA'ME'OR answers that, indeed, the fact that Chizkiyah and Rebbi Yochanan argue only about whether or not these witnesses can become Edim Zomemim shows that their argument is not the same as the argument between Rebbi Akiva and the Chachamim. The Gemara does not challenge this explanation of their argument because the Gemara later (86b), quoting Rav Papa, challenges this explanation of their argument with a stronger question, from a different statement that Chizkiyah himself made.
(b) The CHIDUSHEI HA'RAN answers as follows. If Rebbi Yochanan would have stated merely that the kidnapper is killed based on the testimony of the two sets of witnesses, one would not have known that the first set of witnesses (those who testify about the Geneivah) can be punished as Edim Zomemim. One would have thought that Rebbi Yochanan agrees with the principle of "Davar v'Lo Chatzi Davar." The reason why the kidnapper is Chayav Misah is that each testimony of the two sets of witnesses is considered testimony for a complete event, and not for a "Chatzi Davar." This is because the act of kidnapping is totally independent of the subsequent act of selling the victim. If, however, the first set of witnesses are proven to be Edim Zomemim, Beis Din would not be able to kill them since they did not give testimony that would have caused the kidnapper to be killed (all they said was that he stole a person, but not that he stole and sold a person). Rebbi Yochanan therefore teaches that the witnesses can be killed even if they are found to be Edim Zomemim, because he maintains that the testimony of the witnesses who testify about the kidnapping are considered a single testimony together with the testimony of the witnesses who testify about the sale of the person. Their testimonies together make the kidnapper Chayav Misah.
Why, though, is the kidnapper Chayav Misah based on the combined testimonies of the two sets of witnesses? If the first witnesses can be punished with death if they are found to be Edim Zomemim, then their testimony is not independent of the testimony of the second set of witnesses, but rather it is part and parcel of one whole testimony. This, however, contradicts the principle of "Davar v'Lo Chatzi Davar," and Beis Din should not kill the kidnapper based on their testimony! The Gemara proves from here that Rebbi Yochanan does not agree with the principle of "Davar v'Lo Chatzi Davar," but rather he maintains that even when one set of witnesses testifies about a "Chatzi Davar," the testimony is accepted. (Y. Montrose)

86b----------------------------------------86b

2) WITH WHOM MUST A "ZAKEN MAMREI" DISAGREE IN ORDER TO BE PUNISHED?
OPINIONS: The Mishnah describes how a judge is able to become a Zaken Mamrei. He first approaches other courts and tells them of his ruling, which is counter to the ruling of the Sanhedrin. If the judges of the other courts are unsuccessful at dissuading him from his opinion, he then approaches the Sanhedrin. If they rule against him, he is not permitted to instruct anyone to act in accordance with his view which he insists is correct. If he does instruct someone to act in accordance with his own opinion, and that person indeed conducts himself in that way, then the judge is killed as a Zaken Mamrei.
Must every member of the Sanhedrin disagree with this judge's opinion, or is the ruling of a majority of the Sanhedrin against this judge's opinion enough to make him punishable as a Zaken Mamrei?
(a) The ME'IRI writes that "it seems that one does not become a Zaken Mamrei until he argues with all seventy-one" judges of the Sanhedrin, "but if there was one among them who agreed with his opinion, then he is not killed" as a Zaken Mamrei. He writes that this is the view of many of the earlier Rishonim. (See MARGOLIYOS HA'YAM who suggests a source for this opinion.)
(b) The RAMBAM (in Perush ha'Mishnayos) disagrees and states that the judges of the Sanhedrin discuss the ruling "until all or most agree." This is also the opinion of the RAMBAN (in his commentary to Sefer ha'Mitzvos, Shoresh Rishon, p. 26). (Y. Montrose)