old_contents: def get_price_without_vat(price_to_show, vat_percent):
      raise NotImplementedError()
  
  
  def get_price_without_vat_from_other_valuta(conversion_rate, origin_price,
                                              origin_vat, other_vat):
      raise NotImplementedError()
  
new_contents: def show_pretty_price(value):
      raise NotImplementedError()
  
subject: Use function described in readme