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Home > Vol 27, No 3 (2008)

Victor Kreiman

University of Georgia Department of Mathematics Athens GA 30602 USA

The Richardson variety X _α  ^γ  in the Grassmannian is defined to be the intersection of the Schubert variety X ^γ  and opposite Schubert variety X _α  . We give an explicit Gröbner basis for the ideal of the tangent cone at any T-fixed point of X _α  ^γ  , thus generalizing a result of Kodiyalam-Raghavan (J. Algebra 270(1):28-54, 2003) and Kreiman-Lakshmibai (Algebra, Arithmetic and Geometry with Applications, 2004). Our proof is based on a generalization of the Robinson-Schensted-Knuth (RSK) correspondence, which we call the bounded RSK (BRSK). We use the Gröbner basis result to deduce a formula which computes the multiplicity of X _α  ^γ  at any T-fixed point by counting families of nonintersecting lattice paths, thus generalizing a result first proved by Krattenthaler (Sém. Lothar. Comb. 45:B45c, 2000/2001; J. Algebr. Comb. 22:273-288, 2005).

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