Optical spectroscopy of BL Lac objects: New redshifts and mis-identified sources N. Carangelo, R. Falomo, J. Kotilainen, A. Treves and M.-H. Ulrich A&A, 412 3 (2003) 651-655 Published online: 08 December 2003 DOI: 10.1051/0004-6361:20031519