Represented on March 25, 2017 at Spring Scientific Session, Faculty of Mathematics and Informatics, University of Sofia (Here are the slides in Bulgarian)

   Sent to CFDM 2017 on March 31 (accepted, slides) and to PLS11 on April 19, 2017 (accepted).

   Published on April 20 in Bulgarian and on May 2, 2017 in English.