private CompositeItem convertVarArgs(OperatorNode<ExpressionOperator> ast, int argIdx, CompositeItem out) {
        Iterable<OperatorNode<ExpressionOperator>> args = ast.getArgument(argIdx);
        for (OperatorNode<ExpressionOperator> arg : args) {
            assertHasOperator(arg, ExpressionOperator.class);
            out.addItem(convertExpression(arg));
        }
        return out;
    }
Build a "pure" not, without any positive terms.
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java