Integrity - create field that is a computed sum

Hello -

In Integrity 10.9, I'm trying to create a new field for my documents that is a computed sum of all "Verified By Trace Count" entries in a document.

The field "Verified By Trace Count" related to each requirement is calculated by:

     isEmpty(RelCount("Verified By"),0);

So, at the document level, I was hoping the sum of all these values would simply be:
     sum("Verified By Trace Count");

but that always gave me the error:
"An error occurred parsing the computation expression "sum("Verfied By Trace Count");": MKS124539: sum: Function is an aggregate function, but a non-aggregate computation is being evaluated."

I tried using the aggregate function, but couldn't quite get the syntax right.

Any help would be appreciated.

Is there a document that gives examples on how to use all these computational functions and operators?

Thanks!
John