The subscripts on Ω Ω are used to define the 'state variables' and will be discussed later, when it is argued that the number of particles, n lacks full status as a state variable in this calculation. The integral over configuration space is ℓ ℓ n . As indicated by the underbrace, the integral over velocity space is restricted to the "surface area" of the n − 1 dimensional hypersphere of radius 2 E , and is therefore equal to the "area" of that hypersurface. Thus