Yatza Mimikomo ViLo Birech See Shulchan Aruch 184:A, Rema, that according to Beis Shamai who holds that even Bishogeg Yachzor Limikomo, by Meizid then even "Bidieved Lo Yatza." What is the source in the Gemama for this?
chaim ozer shulman
The BACH suggests the following answer: The Gemara relates the story of the two talmidim, one who did "b'Meizid" like Beis Hillel. That tells us that there is an argument between Beis hShamai and Beis Hillel even in the case of Meized. Sine Beis Hillel holds that b'Meizid he must go back only l'Chatchilah, Beis Shamai must hold that b'Meizid one is not even Yotzei b'Di'eved. See also Biur ha'Gra ibid. DH v'Im.
TAZ suggests another approach.