Daf Yomi - Sukkah 4 - Bent Walls

If a sukkah is higher than twenty amos and a platform is built next to three walls of the sukkah, this will reduce the size of the sukkah and it will be valid. If the platform is built less than four amos away from the walls, it will still be kosher due to the principle of dofan akumah.
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There are two explanations in the Rishonim as to the mechanics of dofan akumah. Rashi understands that the schach which is higher than twenty amos and not on top of the platform is deemed to be an extension of the wall. According to this, one cannot sit under this portion of the sukkah and fulfill his mitzva, for he is sitting under a wall, not under schach.

Other Rishonim explain that since the wall is less than four amos away from the kosher schach and it is normal for a wall to be slanted less than four amos, dofan akumah teaches us that we consider it as if the wall would be touching the platform. According to this, one can sit under the schach that is higher than twenty amos, for since there is a kosher sukkah, there is another principle that any schach protruding out from a valid sukkah is deemed part of the sukkah.

A difference between the two explanations would be if the walls of the sukkah do not touch the schach. We would not be able to apply the principle of dofan akumah according to Rashi's explanation, for since there is a break in the wall, we cannot say that the schach is an extension of the wall. However, we can apply dofan akumah according to the other explanation, for we are connecting the wall to the platform and it doesn't bother us that the wall does not reach the schach.