I need to find all files that trustees 'foo' and 'bar' do not have access to.

Since there are no fields in the Customer search filters for security trustees, i am having to write my search query through the search syntax using the '-' negation operator.

I am successfully able to find all files that are lacking a single trustee from my search with the following:

{LF:LOOKIN="\mainFolder"} 
& {LF:Name="*", Type="D"}
- {LFACE:trustee="foo"}

but I need to be able to find all files that are lacking more than 1 trustee ('foo' and 'bar') in an OR approach. (return a file if 'foo', 'bar', or both are not listed in its security trustees)

{LF:LOOKIN="\mainFolder"} 
& {LF:Name="*", Type="D"}
& {LFACE:trustee<>"foo"}

A single search for excluding 'foo' using the '<>' operator returned incorrect results that included 'foo' as a trustee.

I have unsuccessfully tried the following:

1.
{LF:LOOKIN="\mainFolder"} 
& {LF:Name="*", Type="D"}
- {LFACE:trustee="foo"} | {LFACE:trustee="bar"}

the results from this ^ include files that have both 'foo' and 'bar' (dont want those).

2.
{LF:LOOKIN="\mainFolder"} 
& {LF:Name="*", Type="D"}
-( {LFACE:trustee="foo"} | {LFACE:trustee="bar"} )

the results from this ^ are files that are lacking only both trustees (in an AND approach; does not include files that are only missing one of the trustees)

3.
{LF:LOOKIN="\mainFolder"} 
& {LF:Name="*", Type="D"}
- {LFACE:trustee="foo"} - {LFACE:trustee="bar"}

 same exact results as #2

Would greatly appreciate any suggestions to tinker the query to be able to return the desired results.

Thanks!