Function GREGiso(AnnéeISO%, Semaine%, Optional Jour%)
Application.Volatile ' Facultatif
Dim d As Date
d = DateSerial(AnnéeISO, 1, 7 * (((DateSerial(AnnéeISO, 1, 6) Mod 7) < 4) + Semaine)) - (DateSerial(AnnéeISO, 1, 6) Mod 7)
If AnnéeISO = Year(5 + 7 * (d - 1) \ 7) Then GREGiso = d + 1462 * ThisWorkbook.Date1904 + Jour - (Jour = 0) Else GREGiso = ""
End Function