1. A. Berman, A. Kotzig. Some problems in the theory of graphs with a central symmetry, Preprint CRM-329, Centre de Recherches Mathématiques, Université de Montréal.
2. Lattice Theory;Birkoff,1967
3. Remark on the graphs with a central symmetry;Glivjak;Monatsh. Math.,1970
4. Hadamard matrices of order 16;Hall;J. Philos. Logic Res. Summary,1961
5. Centrally symmetric graphs (in Russian);Kotzig;Czechoslovak Math. J.,1968