% is used in a lot of programming languages as the modulo operator.
\(a\%b=c\iff a\equiv c\mod b\)
which is to say, the remainder upon dividing \(a\) by \(b\) is \(c\).
When you divide any integer by 2, you can get either a remainder of 0 or 1. So in your example, \(x\%2
eq0\) refers to all numbers \(x\) between 1 and 9 that are not perfectly divisible by 2. In other words, \(x\%2
eq0\) refers to those \(x\) that are odd. (This assumes \(B\) is a subset of the integers.)
