INTERSECTION-OF-SETS
====================

syntax: (intersection-of-sets 
              <evaluates-to <set-of A (...)>>
              <evaluates-to <set-of B (...)>>
              [:TYPE <evaluates-to type-name>]
              [:TEST <lisp-type: function>])

        ==> <set-of X (...)>

This function produces the intersection of two sets.

Warning: type checking may cause an error!

example: >(set-to-list (intersection-of-sets
               *cities* *capital-cities* 
               :TYPE 'capital-city))
         (#<CAPITAL-CITY PARIS> #<CAPITAL-CITY 
              BRUESSEL> #<CAPITAL-CITY BERLIN>)