The ESTABLISH  procedure  specifies  a  condition  handler  that
  executes if your program generates operating-system events.

  Syntax:

     ESTABLISH( function-identifier )

  The 'function-identifier'  parameter  must  be  the  name  of  a
  function  that  has  the  ASYNCHRONOUS  attribute.  The function
  passed to ESTABLISH must have two formal array parameters.