it not difficult to denote a function .... for the microcanonical ensemble , the ensemble average of which just yields the entropy. First,the microcanonical phase-space density is given by
on the other hand, we have
formally, the entropy is therefore
to prove this, insert Equation 6.31 into equation 6.33, and bear in mind that p lnp=0 for p=0
the integrand is a constant on the energy shell and can therefore be pulled out of the integral
inserting here equation 5.65 ( without the gibbs factor 1/n!, which has already been omitted in equation 6.30 ), we get