(the lower house) and a Senate (the upper house). The country is divided into 60 electoral districts for the Chamber of Deputies and 19 senatorial constituencies for the Senate. (See Electoral divisions of Chile for details.) Each electoral district and senatorial constituency directly elects two representatives, totaling 120 deputies and 38 senators. Chile is unique in that it was the only country in the world with nationwide two-seat electoral districts. Deputies serve a four-year term and senators serve and eight-year term. Both deputies and senators are eligible for unlimited reelection. Every four years, half the Senate is replaced. In the first Senate after the restoration of democracy in 1990, senators from odd-numbered regions served a four-year term (1990–1994), while senators from even-numbered regions and the Santiago Metropolitan Region served an eight-year term (1990–1998). The senators from odd-numbered regions elected in 1993 served the standard eight-year term (1994–2002). According to the Constitution, parliamentary elections must be held in conjunction with presidential elections. Candidates may register with either the support of a political party or a group of citizens. Party affiliation is optional for candidates supported by a political party, but candidates supported by a group of citizens must not be affiliated with any political party and must collect signatures from independent electors. The number of signatures required is at least 0.5% of the total votes cast in the last Chamber of Deputies election in that electoral district (for a lower-chamber seat) or last Senate election in that senatorial constituency (for a Senate seat). Two or more political parties can form an alliance, known as a "pact," to present up to two candidates per electoral district or senatorial constituency. The candidates do not have to be affiliated with any of the parties in the pact, but they cannot be affiliated with a political party outside of the pact. Political parties that are not part of a pact may present up to two candidates per electoral district or senatorial constituency, and the candidates must be affiliated with that party. In each electoral district and senatorial constituency election, the two entities (pact, political party not part of a pact, or independent candidate not part of a pact) with the most votes each receive one seat, with the leading candidate in each entity taking the seat. To win both seats, the leading entity must receive at least two times as many votes as the second-leading