# Derivative of Heaviside function of two variables

I know that

$\frac{d}{dx} H(x) = \delta(x)$

but if the heaviside function is of two variables, what would the derivative be? I've searched but not found any discussions on this matter. I have an exercise where i need to calculate

$\frac{d}{dt} ( H(x-\xi+ct) - H(x-\xi-ct) )$, where $\xi, c$ are constant.

but as I said, I don't know how it works when there in two variables.

Thanks

Actually, it does not matter that there are two variables. You are only asked to compute the derivative with respect to $t$, so you can (for this computation) assume $x$ to be a constant. Hence, you only have to apply the chain rule to get