Gabriel Sudan was a Romania

Romania

Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

n mathematician

Mathematician

A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

, known for the Sudan function

Sudan function

In the theory of computation, the Sudan function is an example of a function that is recursive, but not primitive recursive. This is also true of the better-known Ackermann function. The Sudan function was the first function having this property to be published....

 (1927), an important example in the theory of computation

Theory of computation

In theoretical computer science, the theory of computation is the branch that deals with whether and how efficiently problems can be solved on a model of computation, using an algorithm...

, similar to the Ackermann function

Ackermann function

In computability theory, the Ackermann function, named after Wilhelm Ackermann, is one of the simplest and earliest-discovered examples of a total computable function that is not primitive recursive...

 (1928).

Gabriel Sudan received his Ph.D.

Ph.D.

A Ph.D. is a Doctor of Philosophy, an academic degree.Ph.D. may also refer to:* Ph.D. , a 1980s British group*Piled Higher and Deeper, a web comic strip*PhD: Phantasy Degree, a Korean comic series* PhD Docbook renderer, an XML renderer...

 from the University of Göttingen

Georg-August University of Göttingen

The University of Göttingen , known informally as Georgia Augusta, is a university in the city of Göttingen, Germany.Founded in 1734 by King George II of Great Britain and the Elector of Hanover, it opened for classes in 1737. The University of Göttingen soon grew in size and popularity...

 in 1925 for his thesis Über die geordneten Mengen ("On the theory of ordered sets"), supervised by David Hilbert

David Hilbert

David Hilbert was a German mathematician. He is recognized as one of the most influential and universal mathematicians of the 19th and early 20th centuries. Hilbert discovered and developed a broad range of fundamental ideas in many areas, including invariant theory and the axiomatization of...

. He taught at the Polytechnic University of Bucharest

Polytechnic University of Bucharest

Universitatea Politehnica din Bucureşti is a technical university in Bucharest, Romania. It was founded in 1864 based on the older technical school of Gheorghe Lazăr and it was renamed "Politehnica" in 1920.-History:...

 from 1941 until his retirement, in 1966.

Sudan constructed the function that bears his name with the same aim as Wilhelm Ackermann

Wilhelm Ackermann

Wilhelm Friedrich Ackermann was a German mathematician best known for the Ackermann function, an important example in the theory of computation....

: to solve in the affirmative a problem raised by Hilbert. The Ackermann and Sudan functions are chronologically the first examples of recursive functions

Recursion (computer science)

Recursion in computer science is a method where the solution to a problem depends on solutions to smaller instances of the same problem. The approach can be applied to many types of problems, and is one of the central ideas of computer science....

 which are not primitive recursive

Primitive recursive function

The primitive recursive functions are defined using primitive recursion and composition as central operations and are a strict subset of the total µ-recursive functions...

.

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