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.