Two extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey Y. I. Izotov, P. Papaderos, N. G. Guseva, K. J. Fricke and T. X. Thuan A&A, 454 1 (2006) 137-141 Published online: 03 July 2006 DOI: 10.1051/0004-6361:20065100