Daf Yomi - Sukkah 7 - Fitting for all Seven Days

The Gemora states that if one made a sukkah on a movuy that has a lechi, it is valid. The same is true regarding a sukkah by passei biroos. Rashi learns that the sukkah is only valid on Shabbos for then we can apply the principle of migu - since it is deemed a wall regarding Shabbos, it is considered a wall in respect for sukkah as well. The Aruch Lenar asks that this should be considered a sukkah that is not fitting for all seven days and it is ruled on daf 23 that this can invalidate a sukkah? He writes that this can explain the opinion of the Rif who rules that it is valid during the week as well.

The Netziv in Merumei Sadeh explains Rashi's opinion why being a valid sukkah only on Shabbos is not in contrast with the principle of the requirement to be fitting for all seven days, for that requirement invalidates a sukkah that can't physically stand erect for seven days for the walls are too weak or the s'chach will dry up, however that a halacha dictates that it will be valid for one day and not the other, that is not a problem.

There is a Gemora on daf 23 that if one makes a sukkah on top of an animal it is not valid at all, for since one cannot utilyze such a sukkah on Shabbos, it is not valid during the week as well, for it must be fitting to use all seven days. This would indicate that a halachic disqualification for one day does invalidate the sukkah? The Netziv answers that this is only true according to the Tanaim that mandate that the sukkah should be permanent and if so, the possuk is not needed to teach us that the walls should be strong, rather the possuk teaches that it must be completely fitting for all seven days. According to the othe rTanaim who maintain that a sukkah can be temporary, they learn the possuk that it must be fitting for all seven days physically, however if halachaically it was invalid for one day, that does not prevent it from being a valid sukkah.