# Simple way of denoting a condition on a long equation

I have a few equations that are rather long. They are 0 if the long part would become negative. Let's say they look something like $$x =\begin{cases} a+b-cd &\quad \text{if}\ \ a+b-cd > 0\\0 &\quad \text{otherwise}.\end{cases}$$ Now I would prefer not to write the whole long part again. Is there a simple way of writing this? I was looking for something like $$x =\begin{cases} a+b-cd &\quad \text{if}\ \ x>0\\0 &\quad \text{otherwise}.\end{cases}$$ In my case there is no way of simplifying the expression $a+b-cd$. Thanks for your help.

• This notation doesn't work because the value of $x$ is still undefined when you compare it to $0$. – Yves Daoust Aug 13 '18 at 9:11

Superscript $\cdot^+$ is the way to go $$x = (a + b - cd)^+ := \max(0, a + b - cd).$$