Rif Succah 10b {Succah 22a continues; 22b}

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10b

{Succah 22a continues}
and whose shade is more than its sun is valid.
If it is thick like the roof of a house, even though the stars are not visible it is valid.

Gemara:
What is means by meduvlelet {thinly}?
Rav said: Scanty covering {too much empty space between one stick and the other}.
And Shmuel said: {Irregular covering} -- one stick up and one stick down.

Rav maintains that meduvlelet is = to meduldelet {scant}, and the Mishna is teaching only one case: a succah which is meduldelet whose shade is more than its sun is valid.
And Shmuel maintains that meduvlelet is = mebulbelet {askew}, and the Mishna is teaching two cases: a succah which is mebulbelet as well as one whose shade is more than its sun is valid.

{Succah 22b}
"whose shade is more than its sun":
The reason is that is shade is more than its sun. Thus if they are in equal portion it is invalid.

And we learnt in a Mishna the first perek: "and if its sun is more than its shade it is invalid." Thus if they are in equal portion is it valid!

This is no question. Here is above {at the point of the schach} and here is below {on the ground}.
If the sun and shade are equal below, it is valid, for it is known that the shade above {by the schach} is more. And if the sun and shade are equal above, it is invalid, for it is known that the sun below is more than the shade.

Rav Papa said: This is what people say: A {hole the size of a} zuz {coin} above is equivalent to a sela below.

Mishna:
If one makes his succah on top of a wagon or on top of a boat, it is valid, and one may ascend to it on Yom Yov.
On top of a tree or upon of a camel, it is valid and one may not ascend to it on Yom Tov.