fix consistency detection of CNF grammar

alib2data/src/grammar/ContextFree/CNF.h

@@ -515,7 +515,7 @@ public:
 	static bool used ( const grammar::CNF < SymbolType > & grammar, const SymbolType & symbol ) {
 		for ( const std::pair < const SymbolType, ext::set < ext::variant < SymbolType, ext::pair < SymbolType, SymbolType > > > > & rule : grammar.getRules ( ) )
 			for ( const ext::variant < SymbolType, ext::pair < SymbolType, SymbolType > > & rhs : rule.second )
-				if ( ( rhs.template is < SymbolType > ( ) && ( rhs.template get < SymbolType > ( ) == symbol ) ) || ( rhs.template get < ext::pair < SymbolType, SymbolType > > ( ).first == symbol ) )
+				if ( ( rhs.template is < SymbolType > ( ) && ( rhs.template get < SymbolType > ( ) == symbol ) ) )
 					return true;
 		return false;
@@ -568,9 +568,13 @@ public:
 			if ( rule.first == symbol )
 				return true;
-			for ( const ext::variant < SymbolType, ext::pair < SymbolType, SymbolType > > & rhs : rule.second )
-				if ( rhs.template get < ext::pair < SymbolType, SymbolType > > ( ).second == symbol )
+			for ( const ext::variant < SymbolType, ext::pair < SymbolType, SymbolType > > & rhs : rule.second ) {
+				if ( rhs.template is < SymbolType > ( ) )
+					continue;
+
+				if ( rhs.template get < ext::pair < SymbolType, SymbolType > > ( ).first == symbol || rhs.template get < ext::pair < SymbolType, SymbolType > > ( ).second == symbol )
 					return true;
+			}
 		}