Affiliation: | 1. Institute of Mathematics, State Academy of Sciences, Pyongyang, Democratic People''s Republic of Korea;2. PGItech Corp., Pyongyang, Democratic People''s Republic of Korea;3. LAGA, Department of Mathematics, University of Paris VIII, 93526 Saint-Denis, France;4. University of Paris XIII, CNRS, LAGA UMR 7539, Sorbonne Paris Cite, 93430 Villetaneuse, France;5. Telecom ParisTech, 75013 Paris, France |