In mathematics, the nil-Coxeter algebra, introduced by Fomin & Stanley (1994), is an algebra similar to the group algebra of a Coxeter group except that the generators are nilpotent.

**
Definition**

The nil-Coxeter algebra for the infinite symmetric group is the algebra generated by \( u_1, u_2, u_3 \(, ... with the relations

\( {\displaystyle {\begin{aligned}u_{i}^{2}&=0,\\u_{i}u_{j}&=u_{j}u_{i}&&{\text{ if }}|i-j|>1,\\u_{i}u_{j}u_{i}&=u_{j}u_{i}u_{j}&&{\text{ if }}|i-j|=1.\end{aligned}}}

These are just the relations for the infinite braid group, together with the relations u2

i = 0. Similarly one can define a nil-Coxeter algebra for any Coxeter system, by adding the relations u2

i = 0 to the relations of the corresponding generalized braid group.

**
References**

Fomin, Sergey; Stanley, Richard P. (1994), "Schubert polynomials and the nil-Coxeter algebra", Advances in Mathematics, 103 (2): 196–207, doi:10.1006/aima.1994.1009, ISSN 0001-8708, MR 1265793

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