Sukka 22 a, b

We begin the daf with a new Mishna.  It teaches that when a sukka is meduvlelet and when the shade is more than its sun, it is fit.  As well, when the roofing is thick and the stars cannot be seen through the roofing at night, the sukka is fit.  First, the rabbis want to understand the meaning of meduvlelet.  Does this refer to an 'impoverished' or thinly roofed sukka?  A sukka in layers, where the reeds cross over each other at specific points?  A disordered sukka? A sparse sukka?  Each of these possibilities is described in some detail.

One of the possibilities is the principle of lower and cast.  This is not explained in our notes, unfortunately.  It seems to refer to a way of categorizing beams that are a certain distance from each other.  Lavud is a comparable principle, but the two are not applied to the same question at the same time.

Amud (b) calls upon halachot learned in Masechet Eiruvin.  Crossbeams are used at alleyways in certain circumstances to allow carrying on Shabbat.  Similarly, a sukka can be rendered fit if crossbeams of certain widths are placed at particular distances to each other in the construction of the sukka.

Rav Pappa teaches about the concept of zuz v'istera, the light is like the zuz coin above and the istera coin below.  A small hole in the roofing of a sukka the size of a zuz can create a spot of sun or shade the size of an istera on the ground below.  Clearly, even with all of these challenging concepts, the rabbis wish to provide people with clear, meaningful direction on the construction of the sukka.

Of note: Beit Hillel rules that a sukka is fit if the roof is thick and the stars cannot be seen; Beit Shammai rules it unfit.

The daf ends with a new Mishna: a sukka built atop a wagon or ship if fit and one may ascend to enter it on the Festival.  However, while a sukka built in a tree or atop of an animal is fit, one may not ascend to enter it on the Festival due to prohibitions against climbing trees or animals on chagim.  The remainder of the Mishna offers guidance on entering sukkot built in these structures when there might be different numbers of entrances on the ground and also higher, on the tree or animal.