Hello,

I'm wondering how I can show that for all functions which satisfy:

$\displaystyle \frac{\partial ^2 f}{\partial x^2} - \frac{d^2 f}{dy^2} = 0$

that the following is true:

$\displaystyle \frac{\partial ^2 f}{\partial s \partial t} = 0$

Where $\displaystyle f(x,y) = f(x(s,t),y(s,t)) = f(s,t)$

Thanks very much for your help

Jon