TELL-INSTANCE-VALUES
====================

syntax: (tell-instance-values 
                        <evaluates-to relation-name>
                        <evaluates-to instance-spec>
                        <set>
                        [:write-dependents 
                          {T | NIL | Var}]
                        [:probe 
                          {T | NIL | :and-do | Var}])

This function adds all elements of the set, which are 
not included yet, to the value set of the instance 
relation. If ':write-dependents' is not set to 
NIL, then the write-dependents will be informed after 
the value set is changed. The value set will be 
returned, when it was changed, otherwise NIL will be 
returned.

example: >(tell-instance-values 'offer Paris {Louvre})
         NIL

         >(tell-instance-values 'offer Paris 
                             {Louvre Centre-Pompidou})
         #<set-of OFFER (...)>