Gerhard Ringel (October 28, 1919 in Kollnbrunn,

Austria Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...

– June 24, 2008 in

Santa Cruz, California Santa Cruz (Spanish language, Spanish for "Holy Cross") is the largest city and the county seat of Santa Cruz County, California, Santa Cruz County, in Northern California. As of the 2020 United States census, 2020 census, the city population ...

) 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, mathematical structure, structure, space, Mathematica ...

. He was one of the pioneers in

graph theory In mathematics and computer science, graph theory is the study of ''graph (discrete mathematics), graphs'', which are mathematical structures used to model pairwise relations between objects. A graph in this context is made up of ''Vertex (graph ...

and contributed significantly to the proof of the

Heawood conjecture In graph theory, the Heawood conjecture or Ringel–Youngs theorem gives a lower bound In mathematics, particularly in order theory, an upper bound or majorant of a subset of some preordered set is an element of that is every element o ...

(now the

Ringel–Youngs theorem 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 ...

), 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 shar ...

. Although born in Austria, Ringel was raised in

Czechoslovakia Czechoslovakia ( ; Czech language, Czech and , ''Česko-Slovensko'') was a landlocked country in Central Europe, created in 1918, when it declared its independence from Austria-Hungary. In 1938, after the Munich Agreement, the Sudetenland beca ...

and attended

Charles University Charles University (CUNI; , UK; ; ), or historically as the University of Prague (), is the largest university in the Czech Republic. It is one of the List of oldest universities in continuous operation, oldest universities in the world in conti ...

before being drafted into the

Wehrmacht The ''Wehrmacht'' (, ) were the unified armed forces of Nazi Germany from 1935 to 1945. It consisted of the German Army (1935–1945), ''Heer'' (army), the ''Kriegsmarine'' (navy) and the ''Luftwaffe'' (air force). The designation "''Wehrmac ...

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 Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

prisoner of war camp. He earned his

PhD A Doctor of Philosophy (PhD, DPhil; or ) is a terminal degree that usually denotes the highest level of academic achievement in a given discipline and is awarded following a course of graduate study and original research. The name of the deg ...

from the

University of Bonn The University of Bonn, officially the Rhenish Friedrich Wilhelm University of Bonn (), is a public research university in Bonn, North Rhine-Westphalia, Germany. It was founded in its present form as the () on 18 October 1818 by Frederick Willi ...

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 a ...

and Ernst Peschl. 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 was founded in West Berlin in 1948 with American support during the early Cold War period as a Western continu ...

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

German student movement The West German student movement (), sometimes called the 1968 movement in West Germany (), was a left-wing social movement that consisted of mass student protests in West Germany in 1968. Participants in the movement later came to be known as ...

, 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 university, public Land-grant university, land-grant research university in Santa Cruz, California, United States. It is one of the ten campuses in the University of C ...

, 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; ) is both a German public research university in Karlsruhe, Baden-Württemberg, and a research center of the Helmholtz Association. KIT was created in 2009 when the University of Karlsruhe (), founde ...

and the

Free University of Berlin The Free University of Berlin (, often abbreviated as FU Berlin or simply FU) is a public university, public research university in Berlin, Germany. It was founded in West Berlin in 1948 with American support during the early Cold War period a ...

. Besides his mathematical skills he was a widely acknowledged

entomologist Entomology (from Ancient Greek ἔντομον (''éntomon''), meaning "insect", and -logy from λόγος (''lógos''), meaning "study") is the branch of zoology that focuses on insects. Those who study entomology are known as entomologists. In ...

. 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

* * *

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 Academic staff of the Free University of Berlin University of California, Santa Cruz faculty Charles University alumni German emigrants to Czechoslovakia Immigrants 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