1 Introduction
  
  HomalgToCAS  is  one of the core packages of the homalg project [hpa10]. But
  as  one  of  the  rather  technical packages, this manual is probably not of
  interest  for  the  average  uers.  The average user will usually not get in
  direct contact with the operations provided by this package.
  
  Quoting  from  the  Appendix  'homalg: The Core Packages and the Idea behind
  their Splitting' of the homalg package manual (--> 'homalg: HomalgToCAS'):
  
  The  package  HomalgToCAS (which needs the homalg package) includes all what
  is  needed to let the black boxes used by homalg reside in external computer
  algebra  systems.  So  as mentioned above, HomalgToCAS is the right place to
  declare   the  three  GAP  representations  external  rings,  external  ring
  elements,  and external matrices. Still, HomalgToCAS is independent from the
  external  computer  algebra  system  with  which  GAP  will  communicate and
  independent of how this communication physically looks like.
  
  
  1.1 HomalgToCAS provides ...
  
      Declaration and construction of
  
            external   objects  (which  are  pointers  to  data  (rings,ring
              elements, matrices, ...) residing in external systems)
  
            external rings (as a new representation for the GAP4-category of
              homalg rings)
  
            external   ring  elements  (as  a  new  representation  for  the
              GAP4-category of homalg ring elements)
  
            external matrices (as a new representation for the GAP4-category
              of homalg matrices)
  
      LaunchCAS:  the  standard  interface used by homalg to launch external
        systems
  
      TerminateCAS:  the  standard  interface  used  by  homalg to terminate
        external systems
  
      homalgSendBlocking:  the  standard  interface  used  by homalg to send
        commands to external systems
  
      External  garbage  collection: delete the data in the external systems
        that became obsolete for homalg
  
      homalgIOMode: decide how much of the communication you want to see