What is a sensible, correct and non-ambiguous way of rephrasing the following?
The numbers a, b and c are not simultaneously positive, negative nor even.
The idea is that the three numbers are not all three positive, they are not all three negative and they are not all three even. Saying it like this is too repetitive, but the first option is silly because it can also be read as saying that each of the numbers is not positive, negative and even at the same time.
This is for a research math paper, by the way. Note that a, b and c are not really numbers for us to apply special properties. They are called numbers merely for illustration here.