On p-almost direct products and residual properties of pure braid groups   of nonorientable surfaces
  We prove that the n th pure braid group of a nonorientable surface (closed or with boundary, but different from RP2) is residually 2-finite. Consequently, this group is residually nilpotent. The key ingredient in the closed case is the notion of p-almost direct product, which is a generalization of the notion of almost direct product. We prove therefore also some results on lower central series and augmentation ideals of p-almost direct products. 
Paolo Bellingeri (LMNO), Sylvain Gervais (LMJL)
math.GT math.GR