Ira Martin Gessel (born 9 April 1951 [1] in Philadelphia, Pennsylvania) is an American mathematician, known for his work in combinatorics. He is a long-time faculty member at Brandeis University and resides in Arlington, Massachusetts.
Gessel studied at Harvard University graduating magna cum laude in 1973. There, he became a Putnam Fellow in 1972, alongside Arthur Rubin and David Vogan. [2]
He received his Ph.D. at MIT and was the first student of Richard P. Stanley. He was then a postdoctoral fellow at the IBM Watson Research Center and MIT. He then joined Brandeis University faculty in 1984. He was promoted to Professor of Mathematics and Computer Science in 1990, became a chair in 1996–98, and Professor Emeritus in 2015.
Gessel is a prolific contributor to enumerative and algebraic combinatorics. He is credited with the invention of quasisymmetric functions in 1984 [3] and foundational work on the Lagrange inversion theorem. As of 2017, Gessel was an advisor of 27 Ph.D. students.
Gessel was elected a Fellow of the American Mathematical Society in the inaugural class of 2012. Since 2015, he is an Associate Editor of the Digital Library of Mathematical Functions . [4]
Gessel has made significant contributions to an area in combinatorics known as lattice walks, which usually take place on the integer lattice and are sometimes confined to the upper right quadrant. An excursion is a lattice walk which starts at the origin and returns to the origin. A lattice excursion in the upper right quadrant with four possible steps, up, down, northeast, and southwest, is now known as a Gessel excursion.
By 2001 Gessel had noted empirically, and conjectured, that the number of Gessel excursions with 2n steps admit a simple hypergeometric closed form. This closed form counting function equation became known as Gessel's lattice path conjecture. A computer aided proof of Gessel's conjecture by Manuel Kauers, Christoph Koutschan, and Doron Zeilberger, was published in 2009. [5]
The 2022 David P. Robbins Prize of the American Mathematical Society was awarded to Alin Bostan, Irina Kurkova, and Kilian Raschel, for their 2017 paper "A human proof of Gessel's lattice path conjecture." [6]
In 1970, while a senior in high school, Ira Gessel and his brother Michael Gessel started a grassroots political organization to end pay toilets in America. [7] The movement was largely successful and was disbanded in 1976.
Combinatorics is a branch of mathematics concerning the study of finite or countable discrete structures.
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Herbert Saul Wilf was an American mathematician, specializing in combinatorics and graph theory. He was the Thomas A. Scott Professor of Mathematics in Combinatorial Analysis and Computing at the University of Pennsylvania. He wrote numerous books and research papers. Together with Neil Calkin he founded The Electronic Journal of Combinatorics in 1994 and was its editor-in-chief until 2001.
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Louis Joseph Billera is a Professor of Mathematics at Cornell University.
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In algebra and in particular in algebraic combinatorics, a quasisymmetric function is any element in the ring of quasisymmetric functions which is in turn a subring of the formal power series ring with a countable number of variables. This ring generalizes the ring of symmetric functions. This ring can be realized as a specific limit of the rings of quasisymmetric polynomials in n variables, as n goes to infinity. This ring serves as universal structure in which relations between quasisymmetric polynomials can be expressed in a way independent of the number n of variables.
In mathematics, a differential poset is a partially ordered set satisfying certain local properties. This family of posets was introduced by Stanley (1988) as a generalization of Young's lattice, many of whose combinatorial properties are shared by all differential posets. In addition to Young's lattice, the other most significant example of a differential poset is the Young–Fibonacci lattice.
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Christoph Koutschan is a German mathematician and computer scientist. He is currently with the Johann Radon Institute for Computational and Applied Mathematics (RICAM) of the Austrian Academy of Sciences.
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