Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
Unprotect
[A2].Locked = UCase([A1]) = "NON"
If Target.Address = "$A$2" Then tmp = [A2]
If Target(1).Address = "$A$1" Then [A2] = IIf(UCase([A1]) = "OUI", tmp, "")
Protect
Application.EnableEvents = True
End Sub