I have an expression that involves the Wigner 3j coefficient:
$\left(\matrix{a&b&0\\0&0&0}\right)^{-1}$
This simplifies to:
$\left[\frac{\left(-1\right)^{a}\delta_{ab}}{\sqrt{2a+1}}\right]^{-1}$
Which, in turn would be:
$\frac{\sqrt{2a+1}}{\left(-1\right)^{a}\delta_{ab}}$
What I'm unsure about is how the Kronecker Delta behaves when it's in the denominator. This would seem to me to indicate that the expression is finite when $a=b$ and infinite otherwise, is that correct?