Sukkah 19: Creative Interpretations

When something comes off a sukkah, it's treated like a sukkah - whatever does that mean? The Gemara offers 4 possibilities, including a discussion of shade vs. sunlight. Also, 2 mishnayot - the first of which is undermined by a contradictory beraita and R. Yosi's practice. The second mishnah allows for sukkah mats for schach, as long as they've been designated for schach use.