Summary of Sunday's shiur

Last night's shiur focused on the new mishna at the top of ו:

The case:
A murder case in which two sets of witnesses each saw a murder take place, with a fifth person, known as the מתרה - the "warner" standing next to the murderer below.  The mishna defines the two groups of witnesses as two separate entities when no one witness in each of the groups sees a witness of the other group.  However, if even one witness of group A sees a witness of group B, they are viewed as one group. 

Ramifications:
According to (a re-worded) Rashi, the נפקא מינה, ramification, bears on the halacha of עדים זוממים.  We know that in a group of witnesses, none are killed כאשר זמם unless all of them are הוזם.  Therefore, if the two sets of witnesses are linked (as explained above) they are deemed to be one group ---and even if two are הוזם, they are 'saved' by virtue of their connection with the two that were not הוזם.  If they do not see each other, then their separate status allows one כת to be executed while the other is saved.  This latter scenario is what is meant by the mishna, when it says הוא והן נהרגין.  He (the accused) is killed because there is still one set of kosher witnesses implicating him; the כת that is הוזם is killed, however, since they were subject to an עמנו הייתם attack edut....

Tosafot adds to the discussion: he points out that if they are deemed to be one group, we also invalidate the edut of all of them based on the presence of one קרוב or פסול. Here, he uses the term נמצא אחד מהם - ie one of the edim was found to be an invalid witness; he then adds what Rashi says, using the term נמצא אחת מהן - one of the groups of edim was found to be זוממת - they are not killed, but rather "saved" by the non-הוזם group.  Tosafot continues to note that if one of the two groups of edim is הוזם ,it also collapses the edut of the other group - explaining that it impacts in a parallel way as does a  קרוב או פסול on an edut of which it is a part.  We inferred from Tosafot, however, that if one of the edim was הוזם, the edut would not collapse.  Why? Whereas a קרוב או פסול is intrinsically problematic (and therefore has the ability to collapse the whole edut) - an עד זומם is irrelevant on his own.   Just as עדים זוממים are punished only when the two of them are הוזם, so, too, a single ed zomem is inconsequential.  Borrowing a concept from ג. - a single ed zomem can still rightfully assert that he is telling the truth and the מזימים are lying - so his presence in an edut of four is innocuous...the accused is killed, none of the edim are executed,and his הוזם status does not collapse the edut!