code: private static <E> int getOccurrences(OWLAxiom ax, Set<Explanation<E>> axiomSets) {
          int count = 0;
          for (Explanation<E> explanation : axiomSets) {
              if (explanation.getAxioms().contains(ax)) {
                  count++;
              }
          }
          return count;
      }
docs: Given an checker and a set of explanations this method determines how many explanations
  contain the checker.
  
  @param ax        The checker that will be counted.
  @param axiomSets The explanations to count from
  @return the number of occurrences of the specified checker in the explanation