I am reading an English translation of the classic book by Gelfond & Linnik: Elementary Methods in the Analytic Theory of Numbers.
Here is the definition of "normal" from the book (page 5 in my copy):
We shall describe the system of numbers $H\subset[0,n]$ as normal if, for any numbers $f \in$ $[1,n]$;$f'\in[1,n]$;$f\notin(H)$;$f'\notin{H}$, we have $f + f' - n$ $\notin H.$
Is this the standard term to describe this situation?
I looked it up in Wikipedia and found a list of where normal is used mathematically. None of the uses listed there seemed to fit the use of Gelfond & Linnik.
If normal is not the standard term, what would be the standard term?