I have a difficult time understanding the following:

there are few shitos about the machlokes between Rav Yehoda and Rav Yosi about Hafsoko. When i first learned the sugya i thought for sure that hafsoko means that since rav yehuda holds one may not start he therefore must stop IMMIDIATLY. but a closer look at the sugya: rashbam and tosfos or anybody else i looked up no one says that one must stop. Rather Hafsoko means:

that one has to stop at night.now first of all what does that have to do with the prohibition of not starting? the chiyuv to stop at night is only because one has to START eating l'shaim shabbos or a reason of the like but it has nothing to do with the prohibition of starting??? secondly why t'ache isn't one mechuyav to stop right away(aspecially with the fact that the gemoro goes into the details of starting before the zman issur or after which i completely don't understand) we always find that if one started b'issur he must stop immidiatly. like if someone started to eat

before A'lois H'ashachar if he started a half hour before he may continue, but if started within half an hour he must stop?

thanks

shmuel from NJ

Shmuel Tannenbaum, NJ, USA