MacRO: Check If WorkBook Open. If Not, Open It.

I did a macro on my mac to transfer a sheet from one workbook to another worbook. It works very well when the destination workbook is open. Therefore I wanted to add some piece of code to check if the destination workbook is open. If not then I wanted the macro to open it before tranfering the sheet. Here is the code I´m using for tranfering the sheet

Sub Transfer_Sluttet()
If ActiveSheet.Index <> Sheets.Count Then
Application.DisplayAlerts = False
Set ws = ActiveSheet
Sheets(ws.Index + 1).Delete
ws.Move Before:=Workbooks("Sluttet.xls").Sheets("sheet2")
'Moves active sheet to beginning of named workbook.
'Replace Test.xls with the full name of the target workbook you want.
Application.DisplayAlerts = True
End If
End Sub

This is the type of macro I useually use on my pc to check if a workbook is open and if not then open it

If IsWorkbookOpened("Filename.xls", "C:Documents and ..................