XML VB.Net

Public Class Example8
    Shared  Sub Main
        Dim doc As System.Xml.XmlDocument
        Dim editor, editor2 As System.Xml.XPath.XPathNavigator
        Dim writer As System.Xml.XmlWriter
        doc = New System.Xml.XmlDocument
        doc.Load("pubs.xml")
        For Each editor In doc.CreateNavigator.Select("/pubs/titles[authors/@au_lname='Green']")
            editor2 = editor.SelectSingleNode("authors[@au_lname!='Green']")
            If Not IsNothing(editor2) Then
                editor2.DeleteSelf()
            End If
            writer = editor.AppendChild()
            writer.WriteStartElement("authors")
            writer.WriteAttributeString("au_lname", "A")
            writer.WriteAttributeString("au_fname", "B")
            writer.Close()
        Next
        doc.Save("output.xml")
    End Sub
End Class