Orateur: Vladimir Verchinine (Université de Montpellier)
Titre: Brunnian braids: topology and algebra.
Résumé:  A Brunnian braid means a braid that becomes trivial after removing any one of its strands. We describe the group of Brunnian braids on a general surface. In the cases when a surface is a sphere or projective plane the group of Brunnian braids is described by means of the homotopy groups of a 2-sphere. Then we study the graded Lie algebra of the descending central series related to Brunnian subgroup of the pure braid group. A presentation of this Lie algebra is obtained.

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