13 External packages
  
  The use of the packages NormalizInterface [GHS14] (an interface to Normalize
  [BIRC14];  or in its absence 4ti2Interface[Gut], and interface to 4ti2[tt]),
  SingularInterface  (an  interface  to  Singular  [DGPS12]; or in its absence
  Singular  [CdG12]);  or  in  its  absence  GradedModules  [BGJ+14] is highly
  recommended  for  many  of the functions presented in this chapter. However,
  whenever  possible a method not depending on these packages is also provided
  (though  slower).  The  package  tests if the user has downloaded any of the
  above  packages,  and if so puts NumSgpsCanUsePackage to true, where Package
  is any of the above.
  
  
  13.1 Using external packages
  
  As  mentioned  above  some  methods  are  specifically  implemented  to take
  advantage  of several external packages. The following functions can be used
  in case these packages have not been loaded prior to numericalsgps.
  
  13.1-1 NumSgpsUse4ti2
  
  NumSgpsUse4ti2(  )  function
  
  Tries  to  load the package 4ti2Interface. If the package is available, then
  it also loads methods implemented using functions in this package.
  
  13.1-2 NumSgpsUse4ti2gap
  
  NumSgpsUse4ti2gap(  )  function
  
  Tries to load the package 4ti2gap. If the package is available, then it also
  loads methods implemented using functions in this package.
  
  13.1-3 NumSgpsUseNormalize
  
  NumSgpsUseNormalize(  )  function
  
  Tries  to  load  the package NormalizInterface. If the package is available,
  then it also loads methods implemented using functions in this package.
  
  13.1-4 NumSgpsUseSingular
  
  NumSgpsUseSingular(  )  function
  
  Tries  to  load  the  package singular. If the package is available, then it
  also loads methods implemented using functions in this package.
  
  To prevent incompatibilities, the package will not load if SingularInterface
  has been already loaded.
  
  13.1-5 NumSgpsUseSingularInterface
  
  NumSgpsUseSingularInterface(  )  function
  
  Tries  to  load  the package SingularInterface. If the package is available,
  then it also loads methods implemented using functions in this package.
  
  To prevent incompatibilities, the package will not load if singular has been
  already loaded.
  
  13.1-6 NumSgpsUseSingularGradedModules
  
  NumSgpsUseSingularGradedModules(  )  function
  
  Tries  to  load the package GradedModules. If the package is available, then
  it also loads methods implemented using functions in this package.
  
  It also creates a ring of rationals NumSgpsRationals.