452  12.  - 

,  ,     .   -
,         -
    .       , -
      .




















[  ]

[ )




. 12.3.       

12.4.2.2.    

    ,   -
 proposition    detennineVacationAppropriate().
,    proposition   operator () =0   
 .       -
 operator ().    ,    
   "", .. ,   -
  .     . 
      --
 :     ,