It is known that the pure braid groups are residually torsion-free nilpotent. This property is however widely open for the most obvious generalizations of these groups, like pure Artin groups and like fundamental groups of hyperplane complements (even reflection ones). In this paper we relate this problem to the faithfulness of linear representations, and prove the residual torsion-free nilpote...

In the early 1970s, Quillen [Qui] noticed a strong connection between 1-parameter formal Lie groups and cohomology theories with a natural theory of Chern classes. The algebraic geometry of these formal Lie groups allowed Morava, Ravenel, and others to make predictions about large scale phenomena in stable homotopy theory, and the resulting theorems completely changed the field. For example, th...

We show that a group is GVZ-group if and only it flat group. the nilpotence class of bounded by number distinct degrees irreducible characters. also certain CM-groups can be characterized as GVZ-groups whose character values lie in prime field.