# Statistical mechanics - density of states

#### ehudhaim

Hi,
I'm studying statistical mechanics from Reif's book.
In his book Reif is reaching the conclusion that the number of states avaiable to a system at energy E (up to some small uncertainty in the energy due to finite observation) with f degrees of freedom is proportional to E^f .
There is a "not so much" of a proof of this lemma in his book, he assumes many things in that so called proof.
could any one please refer me to an exact proof?
By the way, I did an introductionary course in qunatum physics so feel about free to refer me to formal proofs.

Another small question: Does the "a-priori probability" theorem in quantum statistical mechanics comes directly from Von Neumann's equation? Or do I have to postulate something else?

Thank you very much for helping. I am sorry for my bad english.
Ehud.

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