Legal provisions for mandatory referendums at national level

(5) A bill to alter this section, schedule 1 to this Constitution or any of the provisions of this Constitution specified in Part I of that schedule or any of the provisions of the Supreme Court Order specified in Part I1 of that schedule shall not be submitted to the Governor-General for his assent unless-

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 (c) the bill has been approved on a referendum, held in accordance with such provisions as may be made in that behalf by Parliament, by not less than two-thirds of all the votes validly cast on that referendum.