Holomorphic factorization of mappings into SL_n(C)
  We solve Gromov's Vaserstein problem. Namely, we show that a null-homotopic holomorphic mapping from a finite dimensional reduced Stein space into SL_n(C) can be factored into a finite product of unipotent matrices with holomorphic entries. 
Bj\"orn Ivarsson, Frank Kutzschebauch