ON AN ACTION OF THE BRAID GROUP B2g+2 ON THE FREE GROUP F2g
Abstract
We construct an action of the braid group B2g+2 on the free group F2g extending an action of B4 on F2 introduced earlier by Reutenauer and the author. Our action induces a homomorphism from B2g+2 into the symplectic modular group Sp2g(ℤ). In the special case g = 2 we show that the latter homomorphism is surjective and determine its kernel, thus obtaining a braid-like presentation of Sp4(ℤ).
En mi'm alte Kumpel Christophe Reutenauer