  We show that measurements of semi-inclusive $\pi^\pm$ asymmetries on $p$ and
$n$ with polarized and unpolarized target and beams allow, without any
knowledge of the polarized parton densities 1) to test independent
fragmentation and SU(2) symmetry for the polarized sea, and 2) to determine
separately the polarized strange and valence quark densities, and the ratio of
the fragmentation functions
  $D_s^{\pi^+ + \pi^-}/D_u^{\pi^+ +\pi^-}$

High Energy Physics - Phenomenology