has reinforced the view of some that voting for third parties is a pragmatic as well as principled option, as minority governments must rely on smaller parties for their support. In the United Kingdom, Labour became a third party to the Tory (later Conservative) and Whig (later Liberal) parties, gradually replacing the Liberals as one of the two main parties. The Liberals were the third party: followed by the SDP–Liberal Alliance, and later the Liberal Democrats, between the February 1974 and 2015 elections obtained 1–10% of seats forming a third party, albeit with significantly fewer seats. This share of seats is despite gathering around a fifth of votes consistently over the same time period.In the UK there is no president and thus no unifying election to force party mergers and regional two-party systems are formed. This is because Duverger's law says that the number of viable parties is one plus the number of seats in a constituency. In Scotland, Labour and the SNP were the two dominant parties (the Scottish Conservatives experienced a resurgence in the 2017 general election and Scottish Parliament elections), with the SNP replacing the Lib Dems in this role. In southwest England, the Lib Dems face off against the Conservatives; Labour voters may vote for the Lib Dems to prevent a Conservative from winning. Caroline Lucas of the Green Party has held a seat since 2010. Other parties have won seats , but they are either elected outside England, where the British FPTP system is used in parallel to the Welsh and Scottish proportional-representation multiparty democracy or through by-elections (such as the Respect Coalition). Northern Ireland has an entirely separate political system in which neither Labour nor the Liberal Democrats stand candidates; the Conservatives occasionally do but are not competitive. Riker pointed to Canada's regional politics, as well as the U.S. presidential election of 1860, as examples of often temporary regional instability that occurs from time-to-time in otherwise stable two-party systems. While the multiparty system can be seen in the House of Commons of Canada, the highly regionalized parties are evident in the province-by-province examination. Unlike in the United States, where the two major parties are organized and unified at the federal, state and local levels, Canada's federal and provincial parties generally operate as separate organizations. Mathematical proof Duverger's law can be proven mathematically at the limit when the number of voters approaches infinity for one