Classical confined phase volume

context	$\langle \mathcal M, \mathcal H,\pi,\pi_0,{\hat\rho},{\hat\rho}_0\rangle$ … classical microcanonical ensemble
context	$\mathrm{dim}(\mathcal M) = 3N$
context	$\hbar$ … Reduced Planck's constant

definiendum

$\varphi(E):=\frac{1}{h^{3N} N!}\int_{\{\langle{\bf q},{\bf p}\rangle\in \Gamma_{\mathcal M}\ |\ H({\bf q},{\bf p})\le E\}} \mathrm d\Gamma$