Imports System
Imports System.Collections.Generic

' 大文字小文字の違いを無視し、アルファベット順とは逆順にソートするためのIComparer
Class CaseInsensitiveReverseStringComparer
  Implements IComparer(Of String)

  Public Function Compare(ByVal x As String, ByVal y As String) As Integer Implements IComparer(Of String).Compare
    ' StringComparer.OrdinalIgnoreCase.Compareとは逆の結果を返すようにする
    Return -1 * StringComparer.OrdinalIgnoreCase.Compare(x, y)
  End Function
End Class

Class Sample
  Shared Sub Main()
    Dim names() As String = New String() {"Alice", "Bob", "Charlie", "Dave", "Eve"}

    Dim caseSensitiveSet As New SortedSet(Of String)(names, StringComparer.Ordinal)
    Dim reverseCaseInsensitiveSet As New SortedSet(Of String)(names, New CaseInsensitiveReverseStringComparer())

    Console.WriteLine("caseSensitiveSet")
    Console.WriteLine(String.Join(", ", caseSensitiveSet))
    Console.WriteLine(caseSensitiveSet.IsSupersetOf(New String() {"aLiCe", "BOB", "dave"}))
    Console.WriteLine()

    Console.WriteLine("reverseCaseInsensitiveSet")
    Console.WriteLine(String.Join(", ", reverseCaseInsensitiveSet))
    Console.WriteLine(reverseCaseInsensitiveSet.IsSupersetOf(New String() {"aLiCe", "BOB", "dave"}))
  End Sub
End Class

caseSensitiveSet
Alice, Bob, Charlie, Dave, Eve
False

reverseCaseInsensitiveSet
Eve, Dave, Charlie, Bob, Alice
True