Public Function IndexOf( _
   ByVal item As T _
) As Integer

public int IndexOf( 
   T item
)

SetList<int> lista = new SetList<int>(new int[] { 5, 10, 20 });
SetList<int> listb = new SetList<int>(new int[] { 2, 4, 6, 8, 10 });

SetList<int> union = lista.UnionWith(listb);
Assert.AreEqual(7, union.Count);
foreach (int i in union)
    Assert.IsTrue(lista.Contains(i) || listb.Contains(i));

Assert.AreEqual(0, union.IndexOf(2));
Assert.AreEqual(6, union.IndexOf(20));

SetList<int> inter = lista.IntersectWith(listb);
Assert.AreEqual(1, inter.Count);
foreach (int i in inter)
    Assert.AreEqual(10, i);

Dim lista As New SetList(Of Integer)(New Integer() {5, 10, 20})
Dim listb As New SetList(Of Integer)(New Integer() {2, 4, 6, 8, 10})

Dim union As SetList(Of Integer) = lista.UnionWith(listb)
Assert.AreEqual(7, union.Count)
For Each i As Integer In union
    Assert.IsTrue(lista.Contains(i) OrElse listb.Contains(i))
Next

Assert.AreEqual(0, union.IndexOf(2))
Assert.AreEqual(6, union.IndexOf(20))

Dim inter As SetList(Of Integer) = lista.IntersectWith(listb)
Assert.AreEqual(1, inter.Count)
For Each i As Integer In inter
    Assert.AreEqual(10, i)
Next