Private Sub Worksheet_Change(ByVal Target As Range)
If Application.Intersect(Target, Range("F12:F13")) Is Nothing Then Exit Sub
Select Case Target.Address
Case "$F$12"
Application.EnableEvents = False
Range("F13") = IIf(Target.Value = "oui", "non", "oui")
Case "$F$13"
Application.EnableEvents = False
Range("F12") = IIf(Target.Value = "oui", "non", "oui")
End Select
Application.EnableEvents = True
End Sub