6 Serre Quotients Subcategory
  
  This  is  an implementation of a convenience object for Serre quotients. The
  Subcategory  implemented in this file is not a CAP category at all, but only
  a  handler  for the serre quotient construction. It does not contain objects
  or anything useful, it is just a wrapper for the function the Serre quotient
  is based upon.
  
  
  6.1 implementation
  
  6.1-1 FullSubcategoryByMembershipFunction
  
  FullSubcategoryByMembershipFunction( C, func )  operation
  Returns:  a function handler
  
  Creates  an  object  which  handles  the function to create a Serre quotient
  category.  It  can be used instead of the function for Serre quotients. Note
  that the result is *NOT A CATEGORY* and can not be seen as one.