Symbolic Discrete Delta Function

This function takes two integer valued arguments and returns 1 if they are equal and 0 otherwise. The computation is done symbolically so the result is not actually returned as a number but as a symbolic expression for substituting symbolic values if required.

$$
f(a,b) := 1_{a = b},
\mbox{ for } a,b \in Z.
$$

Optional invert-input argument is also provided.