# File lib/ri_cal/fast_date_time.rb, line 193
    def nth_wday_in_year(n, which_wday)
      if n > 0
        first_of_year = change(:month => 1, :day => 1)
        first_in_year = first_of_year.advance(:days => (which_wday - first_of_year.wday + 7) % 7)
        first_in_year.advance(:days => (7*(n - 1)))
      else
        december25 = change(:month => 12, :day => 25)
        last_in_year = december25.advance(:days => (which_wday - december25.wday + 7) % 7)
        last_in_year.advance(:days => (7 * (n + 1)))
      end
    end