We can relate this to the derivative of the entropy with respect to x at constant energy E as follows. Suppose we change x to x + dx. Then Ω Ω ( E ) will change because the energy eigenstates depend on x, causing energy eigenstates to move into or out of the range between E and E + δ δ E . Let's focus again on the energy eigenstates for which d E r d x lies within the range between Y and Y + δ δ Y . Since these energy eigenstates increase in energy by Y dx, all such energy eigenstates that are in the interval ranging from E − Y dx to E move from below E to above E. There are