Sukkah 10 - Sukkah atop another sukkah

If one builds a sukkah atop another sukkah, the upper one is valid, but the bottom is not. Why? The Torah instructed to live in a sukkah, not in a sukkah under another sukkah, and incidentally not in a sukkah under a tree or inside a house. But maybe the logic is just the opposite: the Torah told to live in "huts," so sukkah atop another one is just right! - Look at the spelling of the word "sukkot," it is missing a vav, which implies singular.

Rabbi Yehudah disagrees and says that if there are no tenants in the upper sukkah, then the lower one is valid. That is hard to understand: the sukkah should be valid on its own merits, and the tenants should not matter! Maybe Rabbi Yehudah means that the upper sukkah is not livable? But then it's hard to understand the logic of the first few view who validates the top one.

The truth is that they only argue in the marginal case where the upper sukkah is livable but very shaky. The Sages say that the sukkah must be a temporary dwelling, so the top shaky sukkah is good. Rabbi Yehudah insists that one should make the sukkah his dwelling for seven days, and people don't live in shaky dwellings, so he validates the lower one.

The cottage by Van Gogh