I am trying to search for documents that do not have a relationship/linked document associated with them.  The following syntax returns entries that have a link:

{[Expense Reports]:[CheckNumber]="*"}&{LF:Relationsrc="2"}

I tried subtracting the documents with a link by changing the syntax to:

{[Expense Reports]:[CheckNumber]="*"}-{LF:Relationsrc="2"}

but I get no results.

What am I doing wrong?

Thanks.