Is it possible to create a formula that is fulfilling following conditions, using only elementary functions/arithmetic?

Question

Conditions:

• Variables: X, L
• if X = L result of the formula should be -L otherwise it should be 0

So $$f(X,L)=\begin{cases}-L&X=L\\0&\text X\ne L\end{cases}$$

Is it possible to construct a formula fulfilling these conditions using only elementary arithmetic/functions?

Answer 1

How about $$-L\delta_{ (X, L)}$$ where $\delta$ is the Kronecker $\delta$ function?

Or if that is not elementary enough: $$-L\lim_{ t \to L} \frac {t-L}{t-X}$$