I have some integrals involving Heaviside theta functions of non-trivial arguments, in particular [itex]\theta(1-x^2)[/itex] and [itex]\theta(x^2-1)[/itex]. As x is a radial coordinate it's easy enough for me to break these up by hand, but it's cumbersome for me to implement in Mathematica and I can't work out how I'd go about attacking a more general problem. Is there an expression for [itex]\theta(f(x))[/itex] analagous to [tex]\delta(f(x))=\sum_i{\frac{\delta(x-x_i)}{|g'(x_i)|}}[/tex]?

Thanks in advance.