anchor.diff:      | booleanExpression op=(OR|XOR) booleanExpression       # BooleanAlgebra
       | booleanParam op=(ISNULL|ISNOTNULL)                    # BooleanPostfix
       | op=NOT booleanExpression                              # BooleanNot
  -    //| componentRef                                          # BooleanReference
       | BOOLEAN_CONSTANT                                      # BooleanConstant
       ;
   
  
positive.code: 
  aggregate   : 'aggregate' ;
  
  //booleanExpression : 'booleanExpression' ;
  
  //varID       : 'varId';
  
  //WS          : [ \t\n\t] -> skip ;
  
negative.code:     : componentRef
      | constant
      ;
  
  EQ_OPERATOR : ( EQ | NE | LE | LT | GE | GT ) ;
  EQ : '='  ;
  