Just prove a path to proving the expense approval using T & R Policies:

IF TR-REPORT(Requester, Report, Clerk)
         AND DEPARTMENT-HEAD(Authority) AND Authority ≠ Requester
THEN CAN-APPROVE(Authority, Report, Requester)

IF TR-REPORT(Requester, Report, Clerk)
         AND EXPENSES(Report) > 5000 AND APPROVED(Authority, Report)
          AND CAN-APPROVE(Authority, Report, Requester)
THEN MAY-APPROVE(Clerk, Report)

IF TR-REPORT(Requester, Report, Clerk)
         AND DEPARTMENT-HEAD(Requester) AND Clerk ≠ Requester
THEN MAY-APPROVE(Clerk, Report)