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 FUNCTION to_bool (val IN VARCHAR2)
      RETURN BOOLEAN
   IS
      retval BOOLEAN;
   BEGIN
      IF UPPER (val) IN ('Y', 'YES', 'T', 'TRUE')
      THEN
         retval := TRUE;
      ELSIF UPPER (val) IN ('N', 'NO', 'F', 'FALSE')
      THEN
         retval := FALSE;
      ELSE
         retval := NULL;
      END IF;

      RETURN retval;
   END to_bool;