title: How do search engines merge results from an inverted index?
body: <p>How do search engines merge results from an inverted index?</p>
  
  <p>For example, if I searched for the inverted indexes of the words "dog" and "bat", there would be two huge lists of every document which contained one of the two words.</p>
  
  <p>I doubt that a search engine walks through these lists, one document at a time, and tries to find matches with the results of the lists. What is done algorithmically to make this merging process blazing fast?</p>