
Journal of Lie Theory 20 (2010), No. 1, 003015 Copyright Heldermann Verlag 2010 A Combinatorial Basis for the Free Lie Algebra of the Labelled Rooted Trees Nantel Bergeron Dept. of Mathematics and Statistics, York University, Toronto, Ontario M3J 1P3, Canada bergeron@mathstat.yorku.ca Muriel Livernet LAGA et CNRS, Institut Galilée, Université Paris 13, 99 Av. J.B. Clément, 93430 Villetaneuse, France livernet@math.univparis13.fr [Abstractpdf] \def\calT{{\cal T}} \def\calF{{\cal F}} \def\Lie{{\cal {L}}{\it ie}} \def\N{{\Bbb N}} The preLie operad is an operad structure on the species $\calT$ of labelled rooted trees. A result of F. Chapoton shows that the preLie operad is a free twisted Lie algebra over a field of characteristic zero, that is $\calT = \Lie \circ \calF$ for some species $\calF$. Indeed Chapoton proves that any section of the indecomposables of the preLie operad, viewed as a twisted Lie algebra, gives such a species $\calF$. \par In this paper, we first construct an explicit vector space basis of $\calF[S]$ when $S$ is a linearly ordered set. We deduce the associated explicit species $\calF$, solution to the equation $\calT = \Lie \circ \calF$. As a corollary the graded vector space $(\calF[\{1,\ldots,n\}])_{n\in\N}$ forms a sub nonsymmetric operad of the preLie operad $\calT$. Keywords: Free Lie algebra, rooted tree, preLie operad, Lyndon word. MSC: 18D, 05E, 17B [ Fulltextpdf (213 KB)] for subscribers only. 