Module modMain
    Public Sub Main()
        Const id As String = "{EFBA31DB-A2EE-44bb-955E-830898E66F31}"
 
        Dim t As Threading.Mutex
        Dim created As Boolean
 
        t = New Threading.Mutex(True, id, created)
        If created Then
            MsgBox("Erste Instanz")
            Application.Run(New Form1)
        Else
            MsgBox("Dies ist nicht die erste Instanz")
        End If
 
    End Sub
End Module