premise: Margaret Thatcher was a prime minister in Canada.
hypothesis: Margaret Hilda Thatcher , Baroness Thatcher , ( ; 13 October 1925 -- 8 April 2013 ) was a British stateswoman , who served as Prime Minister of the United Kingdom from 1979 to 1990 and as Leader of the Conservative Party from 1975 to 1990 . She was the longest-serving British prime minister of the 20th century , and the first woman to have held the office .