and Margaret separated in 1977, and were divorced in 1984. When his divorce was finalized in 1984, Trudeau became the first Canadian Prime Minister to become a single parent as the result of divorce. In 1984, Trudeau was romantically involved with Margot Kidder (a Canadian actress famous for her role as Lois Lane in Superman: The Movie and its sequels) in the last months of his prime-ministership and after leaving office. In 1991, Trudeau became a father again, with Deborah Margaret Ryland Coyne, to his only daughter, Sarah. Coyne later stood for the 2013 Liberal Party of Canada leadership election and came fifth in a poll won by Justin. Trudeau began practising judo sometime in the mid-1950s when he was in his mid-thirties, and by the end of the decade, he was ranked ikkyū (brown belt). Later, when he travelled to Japan as Prime Minister, he was promoted to shodan (first-degree black belt) by the Kodokan, and then promoted to nidan (second-degree black belt) by Masao Takahashi in Ottawa before leaving office. Trudeau began the night of his famous "walk in the snow" before announcing his retirement in 1984 by going to judo with his sons. Intellectual contributions Trudeau was a strong advocate for a federalist model of government in Canada, developing and promoting his ideas in response and contrast to strengthening Quebec nationalist movements, for instance the social and political atmosphere created during Maurice Duplessis' time in power. Federalism in this context can be defined as "a particular way of sharing political power among different peoples within a state...Those who believe in federalism hold that different peoples do not need states of their own in order to enjoy self-determination. Peoples ... may agree to share a single state while retaining substantial degrees of self-government over matters essential to their identity as peoples". As a social democrat, Trudeau sought to combine and harmonize his theories on social democracy with those of federalism so that both could find effective expression in Canada. He noted the ostensible conflict between socialism, with its usually strong centralist government model, and federalism, which expounded a division and cooperation of power by both federal and provincial levels of government. In particular, Trudeau stated the following about socialists: Trudeau pointed out that in sociological terms, Canada is inherently a federalist society, forming unique regional identities and priorities, and therefore a federalist model of spending and jurisdictional powers