Inversion of some series of free quasi-symmetric functions
نویسندگان
چکیده
The algebra of Free Quasi-Symmetric Functions FQSym [5] is a graded algebra of noncommutative polynomials whose bases are parametrized by permutations. Under commutative image, it is mapped onto Gessel’s algebra of quasi-symmetric functions, whence its name. Quasi-symmetric functions generalize symmetric functions in a natural way, and many classical results admit quasi-symmetric extensions or analogs. However, very few results resembling symmetric series identities, like those of Schur or Littlewood (see, e.g., [11]) are known. In [15], B. C. V. Ung proves a quasi-symmetric analog of Schur’s identity, and conjectures three further combinatorial inversions of quasisymmetric series, which are even stated at the level of FQSym. In this note, we prove a master identity, which consists in a combinatorial formula for the inverses of the alternating sums of free quasi-symmetric functions of the form Fω(I) where I runs over compositions with parts in a prescribed set C. Here Fσ denotes the standard basis of FQSym (mapped onto Gessel’s fundamental basis), and ω(I) is the longest permutation with descent composition I. Ung’s conjectures boil down to the following special cases : no restriction on the parts, even parts, and all parts equal to 2. Acknowledgements. This project has been partially supported by the grant ANR-06-BLAN-0380. The authors would also like to thank the contributors of the MuPAD project, and especially of the combinat part, for providing the development environment for their research (see [9] for an introduction to MuPAD-Combinat).
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ورودعنوان ژورنال:
- Eur. J. Comb.
دوره 31 شماره
صفحات -
تاریخ انتشار 2010