code: func (s CPUSet) Filter(predicate func(int) bool) CPUSet {
  	b := NewBuilder()
  	for cpu := range s.elems {
  		if predicate(cpu) {
  			b.Add(cpu)
  		}
  	}
  	return b.Result()
  }
docs: // Filter returns a new CPU set that contains all of the elements from this
  // set that match the supplied predicate, without mutating the source set.