rem: bool act( IncidenceBase *incidence, CalendarView *view ) { mView = view; return incidence->accept( *this ); }
add: bool act( Incidence *incidence, CalendarView *view ) { mView = view; return incidence->accept( *this ); }
context:         bool act( IncidenceBase *incidence, CalendarView *view )        {          mView = view;          return incidence->accept( *this );        }