// In header: <boost/icl/functors.hpp>
template<typename Combiner> 
struct conversion {
  // types
  typedef conversion< Combiner >                                                                          type;         
  typedef remove_const< typename remove_reference< typename Combiner::first_argument_type >::type >::type argument_type;
  // public static functions
  static argument_type proversion(const argument_type &);
  static argument_type inversion(const argument_type &);
};