There are two equations defined as:

[math]\frac{d\eta}{dt} = - \psi^n[/math]

[math]\frac{d\eta}{dt} = \frac{1-\psi}{\sigma^2} \frac{1}{\frac{dp(\eta)}{d\eta}}[/math]

The paper then says:

As usual, we may now proceed to eliminate [imath]\psi[/imath] by combining the two equations and thus obtain expressions for the rate which can then integrated to yield a relationship between [imath]\eta[/imath] and [imath]t[/imath].

The paper gives an example for n=1 being:

[math]t=(1-\eta) + \sigma^2 p(\eta)[/math]

For the life of me, I can't figure out how to get past the first stage of combining the equations to get rid of [imath]\psi[/imath]...

Any ideas/help?