# File lib/date.rb, line 613
  def self.valid_commercial? (y, w, d, sg=ITALY)
    if d < 0
      d += 8
    end
    if w < 0
      w = jd_to_commercial(commercial_to_jd(y + 1, 1, 1) + w * 7)[1]
    end
    jd = commercial_to_jd(y, w, d)
    return unless ns?(jd, sg)
    return unless [y, w, d] == jd_to_commercial(jd)
    jd
  end