12.4.    C++ 459

   ,     -"" (
   Y ())     operator ().  
    per?ormance_statement.    -
 proposition-   ,    
.   proposition    ,  -
    .   .

//. . .
trip_announcement ;

if(){

II...  .
}
It...

       ?   
i ? ()         
  bool.      .  ,   -
    ,     , 
.     operator ()  . 
       void*.  -
    .

template<class C> proposition<C>::operator void*(void)
(

return((void*)(TruthValue)) ;

}

     ,  " -
 ",    . ,  
 agent        -
,   ,   ,   
 .   12.13      
  .

//  12.13.  displayTravelPlan()

void agent::displayTravelPlan(void)
{

stack<trip_announcement> Route;

if(Tripl){

Route = Tripl.candidates();

}
if(Trip2)(

Route = Trip2.candidates();

}
if(Trip3){

Route = Trip3.candidates() ;

}

while(!Route.empty())
{

cout  Route.top().origin()  " TO "

 Route.top().destination()  endl;

Route.pop() ;

}
)