Private Sub Worksheet_Change(ByVal Target As Range)
If Application.CountIf([M:M], "monté*") = 0 Then Exit Sub
Dim tablo, i&
tablo = Intersect(UsedRange.EntireRow, [L:M]).Formula
For i = 1 To UBound(tablo)
If LCase(tablo(i, 2)) Like "monté*" Then tablo(i, 1) = ""
Next
Application.EnableEvents = False 'désactive les évènements
Intersect(UsedRange.EntireRow, [L:L]) = tablo
Application.EnableEvents = True 'réactive les évènements
End Sub