code: func Without(full, drop Postings) Postings {
  	if full == EmptyPostings() {
  		return EmptyPostings()
  	}
  
  	if drop == EmptyPostings() {
  		return full
  	}
  	return newRemovedPostings(full, drop)
  }
docs: // Without returns a new postings list that contains all elements from the full list that
  // are not in the drop list.