Sukkah 19a and Sukkah 19b, finishing the discussion of pi tikrah, the ceiling being envisioned as coming down and making a wall, four options in what sechach ha-yotzei is, sechach that extends from the sukkah in some way, the rules of slanted sechach, and whether mats of reeds, large or small, are assumed to be for sechach or for mattresses.
