Spin symmetry in Dirac negative-energy spectrum in density-dependent relativistic Hartree-Fock theory Haozhao Liang, Wen Hui Long, Jie Meng and Nguyen Van Giai Eur. Phys. J. A, 44 1 (2010) 119-124 Published online: 11 March 2010 DOI: 10.1140/epja/i2010-10938-6