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Concept

In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle (in degrees or other units) east or west of a given prime meridian (currently, the IERS Reference Meridian). In other words, it is a coordinate line for longitudes, a line of longitude. The position of a point along the meridian at a given longitude is given by its latitude, measured in angular degrees north or south of the Equator. On a Mercator projection or on a Gall-Peters projection, each meridian is perpendicular to all circles of latitude. Assuming a spherical Earth, a meridian is a great semicircle on Earth's surface. Adopting instead a spheroidal or ellipsoid model of Earth, the meridian is half of a north-south great ellipse. The length of a meridian is twice the length of an Earth quadrant, equal to 20,003.93144 km (12,429.86673 mi) on a modern ellipsoid (WGS 84).

Being

Jean Castex ([ʒɑ̃ kastɛks] ; born 25 June 1965) is a French politician who served as Prime Minister of France from 3 July 2020 to 16 May 2022. He was a member of The Republicans (LR) until 2020. Castex served for twelve years as mayor of the small town of Prades prior to his appointment as prime minister by President Emmanuel Macron. He resigned his post ahead of the 2022 legislative election. After leaving public office, he served as president of the state-owned RATP from 2022 to 2025, and has served as president of the SNCF since November 2025.

Being

Taxus is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. Yews occur around the globe in temperate zones of the northern hemisphere, northernmost in Norway and southernmost in the South Celebes. Some populations exist in tropical highlands. The oldest known fossil species are from the Early Cretaceous.

Concept

Set theory is the branch of mathematical logic that studies sets, which can be informally described as collections of objects. Although objects of any kind can be collected into a set, set theory – as a branch of mathematics – is mostly concerned with those that are relevant to mathematics as a whole. The modern study of set theory was initiated by the German mathematicians Richard Dedekind and Georg Cantor in the 1870s. In particular, Georg Cantor is commonly considered the founder of set theory. The non-formalized systems investigated during this early stage go under the name of naive set theory. After the discovery of paradoxes within naive set theory (e.g. Russell's paradox, Cantor's paradox, and the Burali-Forti paradox, et al.), various axiomatic systems were proposed in the early twentieth century, of which Zermelo–Fraenkel set theory (with or without the axiom of choice) is still the best-known and most studied. Set theory is commonly employed as a foundational system for the whole of mathematics, particularly in the form of Zermelo–Fraenkel set theory with the axiom of choice. Besides its foundational role, set theory also provides the framework to develop a mathematical theory of infinity, and has various applications in computer science (such as in the theory of relational algebra), philosophy, formal semantics, and evolutionary dynamics. Its foundational appeal, together with its paradoxes, and its implications for the concept of infinity and its multiple applications have made set theory an area of major interest for logicians and philosophers of mathematics. Contemporary research into set theory covers a vast array of topics, ranging from the structure of the real number line to the study of the consistency of large cardinals.

Land

Saarland (German: [ˈzaːɐ̯lant] ) is a landlocked federal state of Germany in the southwest of the country. With an area of 2,570 km2 (990 sq mi) and a population of 1 million in 2024, it is the smallest German state in area apart from the city-states of Berlin, Bremen, and Hamburg, and the smallest in population apart from Bremen. Saarbrücken is the state capital and largest city; other cities include Neunkirchen and Saarlouis. Saarland is mainly surrounded by the department of Moselle (Grand Est) in France to the west and south and the neighboring state of Rhineland-Palatinate in Germany to the north and east; it also shares a short border, about 8 kilometres (5 miles) long, with the canton of Remich in Luxembourg to the northwest. Having long been a relatively small part of the long-contested territories along the Franco-German linguistic border, Saarland first gained specific economic and strategic importance in the 19th century due to the wealth of its coal deposits and the heavy industrialization that grew as a result. Saarland was first established as a distinct political entity in 1920 after World War I as the Territory of the Saar Basin, which was occupied and governed by France under a League of Nations mandate. Saarland was returned to Nazi Germany following the 1935 Saar status referendum. After World War II, the territory was occupied by France. It then became the Saar Protectorate on 17 December 1947. After the 1955 Saar Statute referendum, it joined the Federal Republic of Germany as a state on 1 January 1957. Saarland used its own currency, the Saar franc, and postage stamps issued specially for the territory until 1959.