def square_root_term_frequency(document, term)
      count = document.term_count(term)
      if count > 0
        sqrt(count - 0.5) + 1
      else
        0
      end
    end
def square_root_term_frequency(document, term)
      count = document.term_count(term)
      if count > 0
        sqrt(count - 0.5) + 1
      else
        0
      end
    end
Chisholm SQRT