On the Omud Aleph there is a Machloikes Rav Nachman and Rav Shesehes to do with 1 or 2 fields and 1or 2 people with Yerushos."Sof Dovor" we Pasken like Rav Sheshes.However we have a Klal which the Rashbam himself brings only an Omud earlier on 128b D.H. DeRav Nachman that we always Pasken like him BEDINI quoting the Gemoro in Kesuvos 13a.And we find Lemoshol in Gittin 34a that when Rav Nachnan's "Bar Plugtah" is Rav Sheshes we do Pasken like Rav Nachman as in there in Gittin at the bottom of 32b that Bitul BeGet only requires 2 Like Rav Nachman Not Like Rav Sheshes .
So not only (a)why is here different but (b)why didn't the Gemoro or Lekol Hapochus the Rashbam himself comment on it?
Boruch Kahan, London England
Boruch, Shalom Aleichem!
The Gemara here (129b) concludes that the Beraisa cited by Rav Ashi is a Tiyuvta to everyone. The Rashbam (DH Tiyuvta) writes that this means that it is a Tiyuvta to everyone apart from Ravin according to Rebbi Yochanan and Rav Sheshes. Since the Gemara itself states that the opinion of Rav Nachman has been rejected and the opinion of Rav Sheshes has been accepted, we therefore do not follow the standard rule elsewhere in Shas that the Halachah follows Rav Nachman when opposed by Rav Sheshes.