private CompositeItem buildNot(OperatorNode<ExpressionOperator> ast) {
        NotItem notItem = new NotItem();
        notItem.addNegativeItem(convertExpression(ast.getArgument(0)));
        return notItem;
    }
Build a "pure" not, without any positive terms.
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java