Extending an enumeration

  Hi,

  I struggle with a simple problem.  I have two simple types,
both are enumerations, one is a subset of the other.  Lets' say:

    working-days:
      - monday, tuesday, wednesday, thursday, friday
    week-days:
      - { working-days }, saturday, sunday

  I would like to have "week-days" defined as an extension of
"working-days".  Sounds sensible, doesn't it?  But I cannot find
how to do it...

  Any idea?

  Regards,

-- 
Florent Georges
http://fgeorges.org/
http://h2oconsulting.be/