How can I do comparison of two fields with my set analysis?

[#1]

I get the notification   "Error in set modifier expression"    for the expression below.  I am trying to get a count for Work Orders where the Closed date is on or before the required completeion date.

count({$<[WO Close Date.CalendarMonthNum] <= [WO Required Date.CalendarMonthNum], [WO Responsible Planner]= {'Hartsfield*'},[Asset ID] ={'PS-*'}>} distinct [WO ID]

)

[#2]

Try something like this:

count({$<[WO Close Date.CalendarMonthNum] = {"=[WO Close Date.CalendarMonthNum]<=[WO Required Date.CalendarMonthNum]"}, [WO Responsible Planner]= {'Hartsfield*'},[Asset ID] ={'PS-*'}>} distinct [WO ID])

[Gysbert_Wassenaar]

or even:

count({$<[WO Close Date.CalendarMonthNum] = {"<=[WO Required Date.CalendarMonthNum]"}, [WO Responsible Planner]= {'Hartsfield*'},[Asset ID] ={'PS-*'}>} distinct [WO ID])

[#4]

The syntax is correct.  I am not getting an error now.  However,  this set analysis is not retrieving any data.  Thanks for your help.

[#5]

Thanks for your help Gysbert.  The error is gone.  However, there is still no data being retrieved with this set analysis.

[Gysbert_Wassenaar]

It needs a value selected in field [WO Required Date.CalendarMonthNum] to work.