The gemorah at the bottom of yud amud beis says that, in order to invalidate an entire sukkah because its under anothr, the upper sukkah has to be 10 tefachim tall--as opposed to an ohel IN a sukkah, where, if it's "fixed," (kavuah) even if its less than 10 tefachim tall, you can't be under that ohel.
In a sukkah under a sukkah case, the upper sukkah is also "fixed." Why would this upper sukkah not pasel the lower sukkah for being a sukkah under an ohel?
Thanks!
Aaron and Benjy Kaplan, LA, CA
When one Sukah is on top of another Sukah, the Gemara explains that ten Tefachim are required to make the entire bottom Sukah invalid. In contrast, in the case of an Ohel inside a Sukah only the area covered by the Ohel is invalid, not the rest of the Sukah.
All the best,
Yaakov Montrose