code: func Intersect(its ...Postings) Postings {
  	if len(its) == 0 {
  		return EmptyPostings()
  	}
  	if len(its) == 1 {
  		return its[0]
  	}
  
  	l := len(its) / 2
  	a := Intersect(its[:l]...)
  	b := Intersect(its[l:]...)
  
  	if a == EmptyPostings() || b == EmptyPostings() {
  		return EmptyPostings()
  	}
  	return newIntersectPostings(a, b)
  }
docs: // Intersect returns a new postings list over the intersection of the
  // input postings.