anchor.diff:          $condition.setVariable($impliedVariable.variable); }
       //-> ^(IS_CONDITION[$IS_OP] unionType ^(VARIABLE SYNTHETIC_VARIABLE memberName ^(SPECIFIER_EXPRESSION ^(EXPRESSION ^(BASE_MEMBER_EXPRESSION memberName)))))
       | LPAREN i2=IS_OP 
  -      { $condition = new IsCondition($i2); }
  +      ({ $condition = new IsCondition($i2); }
         t2=unionType
         { $condition.setType($t2.type);
           Variable v = new Variable(null);
  
positive.code:       memberName
        { $condition.getVariable().setIdentifier($memberName.identifier); }
        specifier
        { $condition.getVariable().setSpecifierExpression($specifier.specifierExpression); }
        RPAREN
      //-> ^(IS_CONDITION[$IS_OP] unionType ^(VARIABLE unionType memberName specifier))
      ;
  
negative.code:         $condition.setVariable($impliedVariable.variable); }
      //-> ^(EXISTS_CONDITION[$EXISTS] impliedVariable)
      | LPAREN e2=EXISTS 
        ({ $condition = new ExistsCondition($e2); } 
        specifiedVariable 
        { $condition.setVariable($specifiedVariable.variable); })?
        RPAREN
      //-> ^(EXISTS_CONDITION[$EXISTS] specifiedVariable2)
      ;
  