Prof. Dr. Bernd Billhardt

Fachbereich 10 - Mathematik und Naturwissenschaften
Institut für Mathematik
Universität Kassel
Untere Königsstr. 86 (HoPla)
D-34109 Kassel

AG Analysis und Angewandte Mathematik

Raum 2015 (Zweiter Stock)

Tel: +49 -(0)561 -804 -2888
Fax: +49 -(0)561 -804 -3597
Sekretariat: Frau Becker (Tel: +49 -(0)561 -804 -2891)

E-Mail: billhardt@uni-kassel.de


Forschung/Research

Structure theory of  regular semigroups and ordered algebraic structures.

Publikationen/Publications

  1. B. Billhardt, On inverse semigroups the closure of whose set of idempotents is a Clifford semigroup, Semigroup Forum 44 (1992) 320 – 331
  2. B. Billhardt, On a semigroup theoretic generalization of the Kalužnin Krasner theorem and normal extensions of inverse semigroups, Semigroup Forum 44 (1992) 364 – 372
  3. B. Billhardt, On a wreath product embedding and idempotent pure congruences on inverse semigroups, Semigroup Forum 45 (1992) 45 – 54
  4. B. Billhardt, On a wreath product embedding for regular semigroups, Semigroup Forum 46 (1993) 62 – 72
  5. B. Billhardt and M. B. Szendrei, A new class of embeddable E-unitary regular semigroups, in: C. Bonzini, A. Cherubini, C. Tibiletti (Eds.), Algebraic Theory and Applications to Formal Languages and Codes, World Scientific, Singapore, 1993
  6. B. Billhardt, Extensions of regular orthogroups by inverse semigroups, Internat. J. Algebra Comput. 5 (1995) 317 – 342
  7. B. Billhardt and M. B. Szendrei, On quasi-F-orthodox semigroups, Proc. Edinburgh Math. Soc. 38 (1995) 361 – 385
  8. B. Billhardt, Extensions of semilattices by left type-A semigroups, Glasgow Math. J. 39 (1997) 7 – 16
  9. B. Billhardt, On embeddability into a semidirect product of a band by a group, J. Algebra 206 (1998) 40 – 50
  10. B. Billhardt and I. Szittyai, On embeddability of idempotent separating extensions of inverse semigroups, Semigroup Forum 61 (2000) 26 – 31
  11. B. Billhardt, M. B. Szendrei, Associativity of regular semidirect product of existence varieties, J. Austral. Math. Soc, Ser. A 69 (2000) 85 – 115
  12. B. Billhardt, On lambda-semidirect  products by locally R-unipotent semigroups, Acta Sci. Math., 67 (2001) 61 - 76
  13. B. Billhardt, On one sided and naturally lattice ordered inverse semigroups, Semigroup Forum 63 (2001) 422 – 428
  14. B. Billhardt, Embedding locally inverse semigroups into Rees matrix semigroups, Semigroup Forum, 65 (2002) 113 - 127
  15. B. Billhardt, M. B. Szendrei, Weakly E-unitary locally inverse semigroups, J. Algebra, 267 (2003) 559 – 576
  16. B. Billhardt, Expansions of completely simple semigroups, Studia Sci. Math. Hungar. 41 (2004) 39 – 58
  17. B. Billhardt, A factorization of dual prehomomorphisms and expansions of inverse semigroups, Studia Sci. Math. Hungar 41 (2004) 295 - 308
  18. B. Billhardt, Bifree locally inverse semigroups as expansions, J. Algebra 283 (2005) 505 – 521
  19. B. Billhardt, A representation for F-regular semigroups, Semigroup Forum 70 (2005) 243 – 251
  20. B. Billhardt, Regular semigroups each of whose least completely simple congruence classes has a greatest element, Communications in Algebra, 34  (2006) 3629-3641
  21. B. Billhardt, Embedding semigroups with associate subgroups into semidirect products, Communications in Algebra, 36 (2008) 3521-3532.
  22. B. Billhardt, E. Giraldez, P. Marques-Smith, P. Mendes, Associate inverse subsemigroups of regular semigroups, Semigroup Forum 79 (2009) 101-118.
  23. B. Billhardt, E. Giraldez, P. Marques-Smith, P. Mendes, Some orthodox  monoids with associate inverse subsemigroups, Communications in Algebra, 39 (2011) 32-49.
  24. B. Billhardt, E. Giraldez, P. Marques-Smith, P. Mendes, Homomorphisms and congruences of regular semigroups with associate inverse subsemigroup, Periodica Mathematica Hungarica, June 2013, Vol. 66, Issue 2, pp 221-243
  25. B. Billhardt, E. Giraldez, P. Marques-Smith, P. Mendes, The variety of unary semigroups with associate inverse subsemigroup, Semigroup Forum, July 2013
  26. B. Billhardt, E. Giraldez, P. Marques-Smith, P. Mendes, A class of unary semigroups admitting a Rees matrix representation, Semigroup Forum, May 2013
  27. B. Billhardt, K. Sangkhanan, J. Sanwong, W. Sommanee, On subsemigroups of direct powers of L1, Acta Mathematica Hungarica, Dec. 2014
  28. B. Billhardt, E. Laysirikul, K. Sangkhanan, J. Sanwong And W. Sommanee, On R-unipotent semigroups with Π L1-embeddable band of idempotents, Semigroup Forum, 2016, DOI: 10.1007/s00233-015-9732-2.
  29. B. Billhardt, Y. Chaiya, E. Laysirikul, K. Sangkhanan, And J. Sanwong, On left quasi-ample semigroups with Π L1-embeddable band of idempotents, Comm. Algebra, 2017, DOI: 10.1080/00927872.2017.1291811.