Left-wing politics have been particularly strong in municipal government since the 1960s. Voters approved charter amendments that have lessened the penalties for possession of marijuana (1974), and that aim to protect access to abortion in the city should it ever become illegal in the State of Michigan (1990). In 1974, Kathy Kozachenko's victory in an Ann Arbor city-council race made her the country's first openly homosexual candidate to win public office. In 1975, Ann Arbor became the first U.S. city to use instant-runoff voting for a mayoral race. Adopted through a ballot initiative sponsored by the local Human Rights Party, which feared a splintering of the liberal vote, the process was repealed in 1976 after use in only one election. As of August 2009, Democrats hold the mayorship and all council seats. The left tilt of politics in the city has earned it the nickname "The People's Republic of Ann Arbor". Nationally, Ann Arbor is located in Michigan's 12th congressional district, represented by Democrat Debbie Dingell.

Answer this question, if possible (if impossible, reply "unanswerable"): Ann Arbor became the 1st city in the US to what type of voting in the Mayoral race?
instant-runoff