Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Address = "$E$21" Then
Set d = CreateObject("Scripting.Dictionary")
For Each c In [trimestre]
If c.Offset(, -1) = Target.Offset(, -1) Then d(c.Value) = ""
Next c
Target.Validation.Delete
Target.Validation.Add xlValidateList, Formula1:=Join(d.keys, ",")
End If
End Sub