Gerhard Ringel (October 28, 1919 in Kollnbrunn,

Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous c ...

– June 24, 2008 in

Santa Cruz, California Santa Cruz ( Spanish for "Holy Cross") is the county seat and largest city of Santa Cruz County, in Northern California. As of the 2020 census, the city population was 62,956. Situated on the northern edge of Monterey Bay, Santa Cruz is a pop ...

) was a German

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History O ...

. He was one of the pioneers in

graph theory In mathematics, graph theory is the study of ''graphs'', which are mathematical structures used to model pairwise relations between objects. A graph in this context is made up of '' vertices'' (also called ''nodes'' or ''points'') which are conn ...

and contributed significantly to the proof of the

Heawood conjecture In graph theory, the Heawood conjecture or Ringel–Youngs theorem gives a lower bound for the number of colors that are necessary for graph coloring on a surface of a given genus. For surfaces of genus 0, 1, 2, 3, 4, 5, 6, 7, ..., the required ...

(now the Ringel–Youngs theorem), a mathematical problem closely linked with the

four color theorem In mathematics, the four color theorem, or the four color map theorem, states that no more than four colors are required to color the regions of any map so that no two adjacent regions have the same color. ''Adjacent'' means that two regions sh ...

. Although born in Austria, Ringel was raised in Czechoslovakia and attended

Charles University ) , image_name = Carolinum_Logo.svg , image_size = 200px , established = , type = Public, Ancient , budget = 8.9 billion CZK , rector = Milena Králíčková , faculty = 4,057 , administrative_staff = 4,026 , students = 51,438 , underg ...

before being drafted into the Wehrmacht in 1940 (after Germany had taken control of much of what had been Czechoslovakia). After the war Ringel served for over four years in a

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...

prisoner of war camp. He earned his PhD from the

University of Bonn The Rhenish Friedrich Wilhelm University of Bonn (german: Rheinische Friedrich-Wilhelms-Universität Bonn) is a public research university located in Bonn, North Rhine-Westphalia, Germany. It was founded in its present form as the ( en, Rhine ...

in 1951 with a thesis written under the supervision of

Emanuel Sperner Emanuel Sperner (9 December 1905 – 31 January 1980) was a German mathematician, best known for two theorems. He was born in Waltdorf (near Neiße, Upper Silesia, now Nysa, Poland), and died in Sulzburg-Laufen, West Germany. He was a student at ...

and

Ernst Peschl Ernst Ferdinand Peschl (1 September 1906 – 9 June 1986) was a German mathematician. Early life Ernst Peschl came from a family of brewery owners. He was born to Eduard Ferdinand Peschl and his wife, Ulla (née Adler) in 1906. Education a ...

. Ringel started his academic career as professor at the

Free University Berlin The Free University of Berlin (, often abbreviated as FU Berlin or simply FU) is a public research university in Berlin, Germany. It is consistently ranked among Germany's best universities, with particular strengths in political science and ...

. In 1970 he left Germany due to bureaucratic consequences of the

German student movement The West German student movement or sometimes called the 1968 movement in West Germany was a social movement that consisted of mass student protests in West Germany in 1968; participants in the movement would later come to be known as 68ers. T ...

, and continued his career at the

University of California, Santa Cruz The University of California, Santa Cruz (UC Santa Cruz or UCSC) is a public land-grant research university in Santa Cruz, California. It is one of the ten campuses in the University of California system. Located on Monterey Bay, on the edge ...

, having been invited there by his coauthor, John W. T. (Ted) Youngs. He was awarded honorary doctorate degrees from the

Karlsruhe Institute of Technology The Karlsruhe Institute of Technology (KIT; german: Karlsruher Institut für Technologie) is a public research university in Karlsruhe, Germany. The institute is a national research center of the Helmholtz Association. KIT was created in 2009 ...

and the

Free University of Berlin The Free University of Berlin (, often abbreviated as FU Berlin or simply FU) is a public research university in Berlin, Germany. It is consistently ranked among Germany's best universities, with particular strengths in political science and ...

. Besides his mathematical skills he was a widely acknowledged

entomologist Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...

. His main emphasis lay on collecting and breeding butterflies. Prior to his death, he gave his outstanding collection of butterflies to the UCSC Museum of Natural History Collections.Retired mathematics professor Gerhard Ringel gives his world-class butterfly collection to UCSC
, UC Santa Cruz Review, Fall 2006

Publications

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References

* 1919 births 2008 deaths People from Gänserndorf District 20th-century American mathematicians 21st-century American mathematicians 20th-century German mathematicians 21st-century German mathematicians Graph theorists University of Bonn alumni Free University of Berlin faculty University of California, Santa Cruz faculty Charles University alumni Austrian emigrants to Czechoslovakia German emigrants to the United States German military personnel of World War II German prisoners of war in World War II held by the Soviet Union {{US-mathematician-stub