Contemporary dollarisation by either country to the currency of the other or the more involved currency union entailing amalgamation of the central banks and economic regulatory systems of both countries have been proposed and discussed though in no way implemented. Law Both nations adhere to secular common law legal systems acknowledging the rule of law; and the separation of powers. Like the United States and Canada, however, Australia is a federal nation with a written constitution. New Zealand, like the United Kingdom, is a unitary state with parliamentary sovereignty. Australia lacks a treaty with its indigenous peoples, whereas New Zealand has had the Treaty of Waitangi from 1840. In acknowledgement of indigenous land rights including aboriginal title, the National Native Title Tribunal and Waitangi Tribunal in the respective nations take similar jurisdiction and powers. Both judicial systems are now independent of the ultimate authority of the Judicial Committee of the Privy Council. Whereas the Constitution of New Zealand is not one that is either codified or entrenched, the Constitution of Australia has had the Commonwealth of Australia Constitution Act as such an entrenched codification embodying a written constitution. New Zealand contract law is now largely distinct from that of Australia due to the effect of Acts of the New Zealand Parliament promulgated since 1969. Main among them is the wide discretionary power given to New Zealand courts in granting relief. In 2005 and 2006 the Australian House of Representatives Standing Committee on Legal and Constitutional Affairs enquired into the harmonisation of legal systems within Australia, and with New Zealand, with particular reference to those differences that affect trade and commerce. The Committee stated that the already close relationship between Australia and New Zealand should be closer still and that: Key recommendations on the Australia–New Zealand relationship included: Establishment of a trans-Tasman parliamentary committee to monitor legal harmonisation and examine options including closer association or union; Pursuit of a common currency; Offering New Zealand Ministers full membership of Australian ministerial councils; Work to advance harmonisation of the two banking and telecommunications regulation frameworks. New Zealand as an Australian state The 1901 Australian Constitution included provisions to allow New Zealand to join Australia as its seventh state, even after the government of New Zealand had already decided against such a move. The sixth of the initial defining and covering clauses in part provides that: 'The States' shall mean such of the colonies