References
  
  [DENMP12]  Delgado, M., Egri-Nagy, A., Mitchell, J. D. and Pfeiffer, M., Viz
  - a GAP package for drawing GAP objects (2012), ((Under development)).
  
  [DFGSL14]  Delgado,  M., Farrán, J. I., García-Sánchez, P. A. and Llena, D.,
  On the weight hierarchy of codes coming from semigroups with two generators,
  IEEE Trans. Inform. Theory, 60, 1 (2014), 282--295.
  
  [DGSM15] Delgado, M., García-Sánchez, P. A. and Morais, J., NumericalSgps --
  a GAP package for numerical semigroups (2015), ((Version number 1.0)).
  
  [DGSRP16]  Delgado,  M.,  García-Sánchez,  P.  A.  and  Robles-Pérez, A. M.,
  Numerical  semigroups  with  a given set of pseudo-Frobenius numbers, LMS J.
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  [DM08]  Delgado, M. and Morais, J., SgpViz -- a user-friendly GAP package to
  deal with semigroups (2008), ((Version number 0.998)).