It has occurred to me that the operators not only allow to expand the searching power in “positive ways” but also make it possible to search for the absence of some values. To search for a field not to have any value, we need to know all possible values – and this is true for the “seniority” filter. The seniority codes range from 1 to 10.
We know that people without current jobs do not have a seniority value assigned. Therefore, by excluding all the 10 levels, we should find all unemployed. (People without a job are like “dead souls“).