code: public static float countPhraseFrequencies(String indexDir, String A, String B) {
          File indexDir_f = new File(indexDir);
  
          if (!indexDir_f.exists() || !indexDir_f.isDirectory()) {
              System.err.println("Search failed: index directory does not exist");
          } else {
              try {
                  return searchPhrase(indexDir_f, A, B);
              } catch (Exception e) {
                  System.err.println("Unable to search "+indexDir);
                  return 0;
              }
          }
          return 0;
      }
docs: Searches an index given the index directory and counts up the frequncy of the two words used in a phrase.
  
  @param indexDir a String containing the directory where the index is stored
  @param A a {@code String} containing the first word of the phrase
  @param B a {@code String} containing the last word of the phrase
  @return float