When the Australian drafters of the Australian Constitution were deliberating on the form it was to take, they studied the constitutions of a number of countries both republics and monarchies, including Canada, Switzerland and the United States. They were obviously interested in the federal systems established in the United States and Canada and drew ideas from that and also from the US Senate. They were also impressed by the mandatory referendum stipulation for constitutional changes in Switzerland and virtually copied that word by word including the requirement for a double majority (see the question on referendums).