Vaktang Lashkia Masahiro Miyakawa Akihiro Nozaki Grant Pogosyan Ivo G. Rosenberg Semirigid sets of diamond orders. 277-283 1996 156 Discrete Mathematics 1-3 http://dx.doi.org/10.1016/0012-365X(95)00053-Y db/journals/dm/dm156.html#LashkiaMNPR96