I adapted this code for use in LotusScript, one of the languages used by IBM Notes (formerly Lotus Notes) as shown below.
Public Function ExcelSheetExists( _
xlBook As Variant, _ ' Excel workbook object
ByVal strSheetName As String _
) As Boolean
On Error GoTo errHandler
ForAll xlSheet In xlBook.Sheets
If xlSheet.Name = strSheetName Then
ExcelSheetExists = True
Exit Forall
End If
End ForAll
GoTo Done
errHandler:
' Call MyCustomErrorHandler()
Resume Done
Done:
End Function