Public Function EnumerateRange( _
   ByVal start As TKey, _
   ByVal end As TKey _
) As IEnumerable(Of KeyValuePair(Of TKey,TValue))

public IEnumerable<KeyValuePair<TKey,TValue>> EnumerateRange( 
   TKey start,
   TKey end
)

using (BPlusTree<int, string> data = Create(Options))
{
    for (int i = 0; i < 100; i++)
        data.Add(i, i.ToString());

    int ix = 0;
    foreach (KeyValuePair<int, string> kv in data.EnumerateRange(-500, 5000))
        Assert.AreEqual(ix++, kv.Key);
    Assert.AreEqual(100, ix);

    foreach (KeyValuePair<int, int> range in new Dictionary<int, int> { { 6, 25 }, { 7, 25 }, { 8, 25 }, { 9, 25 }, { 22, 25 }, { 28, 28 } })
    {
        ix = range.Key;
        foreach (KeyValuePair<int, string> kv in data.EnumerateRange(ix, range.Value))
            Assert.AreEqual(ix++, kv.Key);
        Assert.AreEqual(range.Value, ix - 1);
    }
}

Using data As BPlusTree(Of Integer, String) = Create(Options)
    Dim i As Integer = 0
    While i < 100
        data.Add(i, i.ToString())
        System.Math.Max(System.Threading.Interlocked.Increment(i),i - 1)
    End While

    Dim ix As Integer = 0
    For Each kv As KeyValuePair(Of Integer, String) In data.EnumerateRange(-500, 5000)
        Assert.AreEqual(System.Math.Max(System.Threading.Interlocked.Increment(ix),ix - 1), kv.Key)
    Next
    Assert.AreEqual(100, ix)

    For Each range As KeyValuePair(Of Integer, Integer) In New Dictionary(Of Integer, Integer)() From { _
        {6, 25}, _
        {7, 25}, _
        {8, 25}, _
        {9, 25}, _
        {22, 25}, _
        {28, 28} _
    }
        ix = range.Key
        For Each kv As KeyValuePair(Of Integer, String) In data.EnumerateRange(ix, range.Value)
            Assert.AreEqual(System.Math.Max(System.Threading.Interlocked.Increment(ix),ix - 1), kv.Key)
        Next
        Assert.AreEqual(range.Value, ix - 1)
    Next
End Using