Bruno Bertrand (1) and Jan Govaerts (2,3) ((1) CP3, UCL,
  Louvain-la-Neuve, Belgium, (2) Department of Physics, University of
  Stellenbosch, Stellenbosch, Rep. South Africa, (3) International Chair in
  Mathematical Physics and Applications (ICMPA-UNESCO), Cotonou, Rep. Benin)