Ira Martin Gessel (born 9 April 1951[1] in Philadelphia, Pennsylvania) is an American mathematician, known for his work in combinatorics.
He is credited with the invention of quasisymmetric functions in 1984[3] and foundational work on the Lagrange inversion theorem.
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.