Strait of Gibraltar
Overview
 
The Strait of Gibraltar (Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

: مضيق جبل طارق) is a narrow strait
Strait
A strait or straits is a narrow, typically navigable channel of water that connects two larger, navigable bodies of water. It most commonly refers to a channel of water that lies between two land masses, but it may also refer to a navigable channel through a body of water that is otherwise not...

 that connects the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 to the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

 and separates Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 from Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

 in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. The name comes from Gibraltar
Rock of Gibraltar
The Rock of Gibraltar is a monolithic limestone promontory located in Gibraltar, off the southwestern tip of Europe on the Iberian Peninsula. It is high...

, which in turn originates from the Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 Jebel Tariq (meaning "Tariq's mountain"), albeit the Arab name for the Strait is Bab el-Zakat or "Gate of Charity". It is also known as the Straits of Gibraltar, or STROG (Strait Of Gibraltar), in naval
Navy
A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 use and as "Pillars of Hercules
Pillars of Hercules
The Pillars of Hercules was the phrase that was applied in Antiquity to the promontories that flank the entrance to the Strait of Gibraltar. The northern Pillar is the Rock of Gibraltar in the British overseas territory of Gibraltar...

" (Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

: Ηράκλειες Στήλες) in the ancient world.

Europe and Africa are separated by 7.7 nmi (14.3 km; 8.9 mi) of ocean at the strait's narrowest point.
Encyclopedia
The Strait of Gibraltar (Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

: مضيق جبل طارق) is a narrow strait
Strait
A strait or straits is a narrow, typically navigable channel of water that connects two larger, navigable bodies of water. It most commonly refers to a channel of water that lies between two land masses, but it may also refer to a navigable channel through a body of water that is otherwise not...

 that connects the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 to the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

 and separates Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 from Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

 in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. The name comes from Gibraltar
Rock of Gibraltar
The Rock of Gibraltar is a monolithic limestone promontory located in Gibraltar, off the southwestern tip of Europe on the Iberian Peninsula. It is high...

, which in turn originates from the Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 Jebel Tariq (meaning "Tariq's mountain"), albeit the Arab name for the Strait is Bab el-Zakat or "Gate of Charity". It is also known as the Straits of Gibraltar, or STROG (Strait Of Gibraltar), in naval
Navy
A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 use and as "Pillars of Hercules
Pillars of Hercules
The Pillars of Hercules was the phrase that was applied in Antiquity to the promontories that flank the entrance to the Strait of Gibraltar. The northern Pillar is the Rock of Gibraltar in the British overseas territory of Gibraltar...

" (Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

: Ηράκλειες Στήλες) in the ancient world.

Europe and Africa are separated by 7.7 nmi (14.3 km; 8.9 mi) of ocean at the strait's narrowest point. The Strait's depth ranges between 300 and 900 m (984.3 and 2,952.8 ft) which possibly interacted with the lower mean sea level of the last major glaciation 20,000 years before present when the level of the sea was believed to be lower by 110–120 m (360.9–393.7 ft). Ferries cross between the two continents every day in as little as 35 minutes. The Spanish side of the Strait is protected under El Estrecho Natural Park
El Estrecho Natural Park
El Estrecho Natural Park is a natural park in Spain, located on the northern side of the Strait of Gibraltar....

.

Location

On the northern side of the Strait is Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 and Gibraltar
Gibraltar
Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

 (a British overseas territory in the Iberian Peninsula
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...

), while on the southern side is Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

 and Ceuta
Ceuta
Ceuta is an autonomous city of Spain and an exclave located on the north coast of North Africa surrounded by Morocco. Separated from the Iberian peninsula by the Strait of Gibraltar, Ceuta lies on the border of the Mediterranean Sea and the Atlantic Ocean. Ceuta along with the other Spanish...

 (a Spanish exclave in North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...

). Its boundaries were known in antiquity as the Pillars of Hercules
Pillars of Hercules
The Pillars of Hercules was the phrase that was applied in Antiquity to the promontories that flank the entrance to the Strait of Gibraltar. The northern Pillar is the Rock of Gibraltar in the British overseas territory of Gibraltar...

. There are several islets, such as the disputed
Territorial dispute
A territorial dispute is a disagreement over the possession/control of land between two or more states or over the possession or control of land by a new state and occupying power after it has conquered the land from a former state no longer currently recognized by the new state.-Context and...

 Isla Perejil
Isla Perejil
For the armed conflict, see Perejil Island crisisThe Perejil Island is a small, uninhabited rocky islet located in the South shore of the Strait of Gibraltar very close to Morocco. Its sovereignty is disputed between Spain and Morocco...

, that are claimed by both Morocco and Spain.

Due to its location, the Strait is commonly used for illegal immigration
Illegal immigration
Illegal immigration is the migration into a nation in violation of the immigration laws of that jurisdiction. Illegal immigration raises many political, economical and social issues and has become a source of major controversy in developed countries and the more successful developing countries.In...

 from Africa to Europe.

Extent

The International Hydrographic Organization
International Hydrographic Organization
The International Hydrographic Organization is the inter-governmental organisation representing the hydrographic community. It enjoys observer status at the UN and is the recognised competent authority on hydrographic surveying and nautical charting...

 defines the limits of the Strait of Gibraltar as follows:

On the West. A line joining Cape Trafalgar
Cape Trafalgar
Cape Trafalgar is a headland in the Province of Cádiz in the south-west of Spain. It lies on the shore of the Atlantic Ocean, northwest of the Strait of Gibraltar...

 to Cape Spartel
Cape Spartel
Cape Spartel is a promontory in Morocco about above sea level at the entrance to the Strait of Gibraltar, 12 km West of Tangier. It is frequently but incorrectly referred as the northernmost point of Africa, which is instead Ras ben Sakka, Tunisia....

.

On the East. A line joining Europa Point

Europa Point
Europa Point, also called Great Europa Point, is the southernmost point of Gibraltar. At the end of Rock of Gibraltar, the area is flat and occupied by such features as a playing field and a few buildings...

 to P. Almina
Península de Almina
The Península de Almina is a peninsula making up much of the eastern part of the Spanish city of Ceuta in Africa. It is dominated by the peak of Monte Hacho. The peninsula contains Ceuta's easternmost point, Punta Almina, and is connected to the rest of Ceuta by an isthmus barely 100 metres in...

 (35°54′N 5°18′W).

Geology

Around 5.9 million years ago, the connection between the Mediterranean Sea and the Atlantic Ocean along the Betic
Betic corridor
The Betic Corridor, or North-Betic Strait, was a strait of water connecting the Mediterranean Sea with the Atlantic Ocean that once separated the Iberian plate from the Eurasian plate through the Betic Cordillera...

 and Rifan Corridor was progressively restricted until its total closure, effectively causing the salinity of the Mediterranean to periodically fall within the gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

 and salt deposition range, during what is known as the Messinian Salinity Crisis
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...

. In this water chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 environment, dissolved mineral concentrations, temperature and stilled water currents combined properly and occurred regularly to precipitate many mineral salts in sea floor bedded layers. The resultant accumulation of various huge salt and mineral deposits about the Mediterranean basin are directly linked to this era. It is believed that this process took a short time, by geological standards, lasting between 500,000 and 600,000 years.

It is estimated that, were the straits closed even at today's higher sea level, most water in the Mediterranean basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...

 would evaporate within only a thousand years, as it is believed to have done then, and such an event would lay down similar mineral deposits as those such as the salt mines now found under the sea floor off Sicily
Sicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

.

After a lengthy period of restricted intermittent or no water exchange between the Atlantic Ocean and Mediterranean basin, approximately 5.33 million years ago, the Atlantic-Mediterranean connection was completely reestablished through the Strait of Gibraltar by the Zanclean flood
Zanclean flood
The Zanclean flood is a flood theorized to have refilled the Mediterranean Sea 5.33 million years ago, at the beginning of the Zanclean age, between the Miocene and Pliocene, which ended the Messinian salinity crisis...

, and has remained open ever since. The strait is expected to close again as the African Plate moves northward relative to the Eurasian Plate, but on geological rather than human timescales.

History

(For full articles on the history of the north Gibraltar shore, see History of Gibraltar
History of Gibraltar
The history of Gibraltar portrays how The Rock gained an importance and a reputation far exceeding its size, influencing and shaping the people who came to reside here over the centuries.-Prehistoric:...

 or History of Spain
History of Spain
The history of Spain involves all the other peoples and nations within the Iberian peninsula formerly known as Hispania, and includes still today the nations of Andorra, Gibraltar, Portugal and Spain...

. For the full article on the history of the south Gibraltar shore, see History of Morocco
History of Morocco
The History of Morocco spans over 12 centuries, without considering the Classical antiquity. The country was first unified by the Idrisid dynasty in 780, representing the first Islamic state in Africa autonomous from the Arab Empire. Under the Almoravid dynasty and the Almohad dynasty, Morocco...

.)


Evidence of the first human habitation of the area by Neanderthal
Neanderthal
The Neanderthal is an extinct member of the Homo genus known from Pleistocene specimens found in Europe and parts of western and central Asia...

s dates back to 125,000 years ago. In fact, it is believed that the Rock of Gibraltar
Rock of Gibraltar
The Rock of Gibraltar is a monolithic limestone promontory located in Gibraltar, off the southwestern tip of Europe on the Iberian Peninsula. It is high...

 may have been one of the last outposts of Neanderthal habitation in the world, with evidence of their presence there dating to as recently as only 24,000 years ago.
Archaeological evidence of Homo sapiens habitation of the area dates back to ca. 40,000 years ago.

Beginning in 1492, the straits began to play a certain cultural role in acting as a barrier against cross-strait conquest and the flow of culture and language that would naturally follow such a conquest. In that year, the last Muslim government north of the straits was overthrown by a Spanish force. Since that time, the straits have come to foster the development of two very distinct and varied cultures on either side of the straits.

On the northern side, the Christian/European culture has remained dominant (as it used to be in the southern side too), along with the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 based Spanish language
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...

, while on the southern side, the markedly different Muslim-Arabic/Mediterranean culture came to dominate later, along with the Arabic language. For the last 500 years, religious and cultural intolerance, more than the small travel barrier that the straits present, has come to act as a powerful enforcing agent of the cultural separation that exists between these two groups.

The small British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 enclave of the city of Gibraltar
Gibraltar
Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

 presents a third cultural group found in the straits. This enclave was first established in 1704 and has since been used by Britain to act as a surety for control of the sea lanes into and out of the Mediterranean.

Communications

The Strait is an important shipping route
Shipping route
A shipping route is a trade route used by merchant ships.Early routes usually were coastal in nature as navigators had to rely on the coastal landmarks...

 from the Mediterranean to the Atlantic. There are ferries that operate between Spain and Morocco across the strait, as well as between Spain and Ceuta
Ceuta
Ceuta is an autonomous city of Spain and an exclave located on the north coast of North Africa surrounded by Morocco. Separated from the Iberian peninsula by the Strait of Gibraltar, Ceuta lies on the border of the Mediterranean Sea and the Atlantic Ocean. Ceuta along with the other Spanish...

 and Gibraltar
Gibraltar
Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

 to Tangier
Tangier
Tangier, also Tangiers is a city in northern Morocco with a population of about 700,000 . It lies on the North African coast at the western entrance to the Strait of Gibraltar where the Mediterranean meets the Atlantic Ocean off Cape Spartel...

.

Tunnel across the strait

In December 2003, Spain and Morocco agreed to explore the construction of an undersea
Underwater
Underwater is a term describing the realm below the surface of water where the water exists in a natural feature such as an ocean, sea, lake, pond, or river. Three quarters of the planet Earth is covered by water...

 rail
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

 tunnel
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...

 to connect their rail systems across the Strait. The gauge of the rail would be 1435 millimetre to match the proposed construction and conversion of significant parts of the existing broad gauge system to standard gauge
Standard gauge
The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

.

Special flow and wave patterns

The Strait of Gibraltar serves to directly link the Atlantic Ocean to the Mediterranean Sea. As such, this direct linkage creates certain unique flow and wave patterns. These unique patterns are created due to the interaction of various regional and global evaporative forces, tidal forces, and wind forces.

Inflow and outflow

Through the strait, water generally flows more or less continually in both an eastward and a westward direction. A smaller amount of deeper saltier and therefore denser waters continually work their way westwards (the Mediterranean outflow), while a larger amount of surface waters with lower salinity and density continually work their way eastwards (the Mediterranean inflow). These general flow tendencies may be occasionally interrupted for brief periods to accommodate temporary tidal flow requirements, depending on various lunar and solar alignments. Still, on the whole and over time, the balance of the water flow is eastwards, due to an evaporation rate within the Mediterranean basin higher than the combined inflow of all the rivers that empty into it. The shallow Camarinal Sill
Camarinal Sill
The Camarinal Sill is the sill separating the Mediterranean Sea and the Atlantic Ocean.This threshold is the shallowest seafloor pass between the Iberian Peninsula and Africa. It is located near the Gibraltar Strait and the Espartel Sill, at , at an elevation of −280 m. Marine waters must...

 of the Strait of Gibraltar, which forms the shallowest point within the strait, acts to limit mixing between the cold, less saline Atlantic water and the warm Mediterranean waters. The Camarinal Sill is located at the far western end of the strait.

The Mediterranean waters are so much saltier than the Atlantic waters that they sink below the constantly incoming water and form a highly saline (thermohaline
Thermohaline circulation
The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

, both warm and salty) layer of bottom water. This layer of bottom-water constantly works its way out into the Atlantic as the Mediterranean outflow. On the Atlantic side of the strait, a density boundary separates the Mediterranean outflow waters from the rest at about 100 m (328.1 ft) depth. These waters flow out and down the continental slope, losing salinity, until they begin to mix and equilibrate more rapidly, much further out at a depth of about 1000 m (3,280.8 ft). The Mediterranean outflow water layer can be traced for thousands of kilometres west of the strait, before completely losing its identity.

During the Second World War
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, German U-boats used the currents to pass into the Mediterranean Sea without detection, by maintaining silence with engines off. From Sept 1941 to May of 1944 Germany managed to send 62 U-boats into the Mediterranean. All these boats had to navigate the British-controlled Strait of Gibraltar where 9 U-boats were sunk while attempting passage and 10 more had to break off their run due to damages. No U-boats ever made it back into the Atlantic and all were either sunk in battle or scuttled by their own crews.

Internal waves

Internal wave
Internal wave
Internal waves are gravity waves that oscillate within, rather than on the surface of, a fluid medium. They are one of many types of wave motion in stratified fluids . A simple example is a wave propagating on the interface between two fluids of different densities, such as oil and water...

s (waves at the density boundary layer) are often produced by the strait. Like traffic merging on a highway, the water flow is constricted in both directions because it must pass over the Camarinal Sill. When large tidal flows enter the Strait and the high tide relaxes, internal waves are generated at the Camarinal Sill and proceed eastwards. Even though the waves may occur down to great depths, occasionally the waves are almost imperceptible at the surface, at other times they can be seen clearly in satellite imagery. These internal waves continue to flow eastward and to refract around coastal features. They can sometimes be traced for as much as 100 km (62.1 mi), and sometimes create interference patterns with refracted waves.

Power generation

Some studies have proposed the possibility of erecting tidal power generating stations within the strait, to be powered from the predictable current at the strait.

In the 1920s and 1930s, the Atlantropa
Atlantropa
Atlantropa, also referred to as Panropa, was a gigantic engineering and colonization project devised by the German architect Herman Sörgel in the 1920s and promulgated by him until his death in 1952...

 project proposed damming the strait to generate large amounts of electricity and lower the sea level of the Mediterranean by several hundreds of meters to create large new lands for settlement.

See also

  • List of straits
  • Mediterranean Basin
    Mediterranean Basin
    In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...

  • Strait of Gibraltar crossing
    Strait of Gibraltar crossing
    A Strait of Gibraltar crossing is a hypothetical bridge or tunnel spanning the Strait of Gibraltar that would connect Europe to Africa.The Spanish and Moroccan governments appointed a a to investigate the feasibility of linking the two continents...

  • Atlantropa
    Atlantropa
    Atlantropa, also referred to as Panropa, was a gigantic engineering and colonization project devised by the German architect Herman Sörgel in the 1920s and promulgated by him until his death in 1952...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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