At least one of these variables is equal to something

Question

I have two variables $a$ and $b$, at least one of these variables must be equal to some constant, call it $c$.

If $a$ = $c$, then $b$ could be anything, including $c$. Or, if $b$ = $c$, then $a$ could be anything, including $c$.

Do I write that as such: $\exists (a,b) = 0$?

I suspect that isn't correct.

Answer 1

You can write $$ a=c\; \vee\, b=c. $$