Syntax:  SET DUPLICATE INCLUSIONS processing_state

  En(dis)ables special processing of include file symbols and
  occurrences.

  SET DUPLICATE INCLUSIONS HIDDEN causes queries to recognize include
  file symbols and occurrences; this will eliminate duplicate
  occurrences and symbols resulting from multiples inclusions of a
  single include file.  SET DUPLICATE INCLUSIONS VISIBLE disables this
  recognition.