12.4.    C++ 445

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  ( 12.1).

//  12.1.   

template<class C> class proposition (

//. . .

protected:

list<C> UniverseOfDiscourse;

bool TruthValue;

public:

virtual bool operator()(void) = 0;

bool operator&&(proposition &X) ;

bool operator]|(proposition &X) ;

bool operator||(bool X) ;

bool operator&&(bool X) ;

operator void*() ;

bool operator!(void) ;

bool possible(proposition &X);

bool necessary(proposition &X);

void universe(list<0 &X);

//. . .
};

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  .  . 12.4 ,    -
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 proposition (.  12.1)    
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     proposition     -
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    proposition:

virtual bool operator()(void) = 0;