Problems with default value

Thanx again for your help.

I read about FRL, and I am interested to "make it alive" in PowerLoom. 

I create Frame definition:
There's HUMAN frame with one slot, NAME.
There's STUDENT-FTI frame with one slot, DEPARTMENT. STUDENT-FTI is AKO HUMAN.
DEPARTMENT slot has default value "FTI". NAME slot is "inherited" from HUMAN
frame.
There's STUDENT frame with one slot, STUDENT_ID. STUDENT is AKO STUDENT-FTI.
NAME and DEPARTMENT slot are "inherited" from STUDENT-FTI frame.

Then I create this definition. As usual (again...sorry), I face a problem. I
have 
problem with default value here....
This is my definition (from ";;===START" until ";;===STOP")

;;===START
(clear-module pl-user)

;;(FASSERT HUMAN
;;	(NAME ($REQUIRE (STRING :SLOT)))
;;	(CLASSIFICATION ($VALUE (GENERIC)))
;;).

(clear-module pl-user)

(defconcept HUMAN (?HUMAN))
(deffunction HUMAN_NAME ((?HUMAN HUMAN)) :-> (?NAME STRING))
(defrelation HUMAN-NAME ((?NAME STRING)(?HUMAN HUMAN))
	:<<=>> (= (HUMAN_NAME ?HUMAN) ?NAME))

;;(FASSERT STUDENT-FTI
;;	(AKO ($VALUE (HUMAN)))
;;	(DEPARTMENT ($DEFAULT (FTI))
;;		  ($REQUIRE (STRING :SLOT)))
;;	(CLASSIFICATION ($VALUE (GENERIC)))
;;).

(defconcept STUDENT-FTI ((?HUMAN HUMAN)))
(defrelation STUDENT-FTI-NAME ((?NAME STRING)(?STUDENT-FTI STUDENT-FTI))
	:<<=>> (= (HUMAN_NAME ?STUDENT-FTI) ?NAME))
(deffunction STUDENT-FTI_DEPARTMENT ((?STUDENT-FTI STUDENT-FTI)) 
	:-> (?DEPARTMENT STRING))
(defrelation STUDENT-FTI-DEPARTMENT (?DEPARTMENT (?STUDENT-FTI STUDENT-FTI))
	:<<=>> (= (STUDENT-FTI_DEPARTMENT ?STUDENT-FTI) ?DEPARTMENT))

(presume 
	(=> (STUDENT-fti ?STUDENT-fti) 
	    (STUDENT-fti-DEPARTMENT "FTI" ?STUDENT-fti)))

;;(FASSERT STUDENT
;;	(AKO ($VALUE (STUDENT-FTI)))
;;	(STUDENT_ID ($REQUIRE (INTEGER :SLOT)))
;;).

(defconcept STUDENT ((?STUDENT-FTI STUDENT-FTI)))
(deffunction STUDENT_STUDENT_ID ((?STUDENT STUDENT)) :-> (?STUDENT_ID INTEGER))
(defrelation STUDENT-STUDENT_ID ((?STUDENT_ID INTEGER)(?STUDENT STUDENT))
	:<<=>> (= (STUDENT_STUDENT_ID ?STUDENT) ?STUDENT_ID))
(defrelation STUDENT-NAME ((?NAME STRING)(?STUDENT STUDENT))
	:<<=>> (= (HUMAN_NAME ?STUDENT) ?NAME))
(defrelation STUDENT-DEPARTMENT (?DEPARTMENT (?STUDENT STUDENT))
	:<<=>> (= (STUDENT-FTI_DEPARTMENT ?STUDENT) ?DEPARTMENT))

;;(FINSTANTIATE 'STUDENT 'RIDWAN).
;;(FPUT 'RIDWAN 'NAME '$VALUE 'RIDWAN).
;;(FPUT 'RIDWAN 'CLASSIFICATION '$VALUE 'INDIVIDUAL).
;;(FPUT 'RIDWAN 'STUDENT_ID '$VALUE '13599066).

(assert (STUDENT ridwan))
(assert (STUDENT-NAME "ridwan" ridwan))
(assert (STUDENT-STUDENT_ID 13599066 ridwan))

;;(FINSTANTIATE 'STUDENT 'HERU).
;;(FPUT 'HERU 'NAME '$VALUE 'HERU).
;;(FPUT 'HERU 'CLASSIFICATION '$VALUE 'INDIVIDUAL).
;;(FPUT 'HERU 'STUDENT_ID '$VALUE '13599009).

(assert (STUDENT heru))
(assert (STUDENT-NAME "Heru S.H." Heru))
(assert (STUDENT-STUDENT_ID 13599009 heru))

;;===STOP

Then I do some information retrieval, such as this one... (from ";;===START"
until ";;===STOP"

;;===START
|= (RETRIEVE ALL (?x) (STUDENT ?x))

Warning: INTERNAL ERROR: DON'T KNOW YET HOW TO EQUATE THINGS BY DEFAULT.
Warning: INTERNAL ERROR: DON'T KNOW YET HOW TO EQUATE THINGS BY DEFAULT.
Warning: INTERNAL ERROR: DON'T KNOW YET HOW TO EQUATE THINGS BY DEFAULT.
Warning: INTERNAL ERROR: DON'T KNOW YET HOW TO EQUATE THINGS BY DEFAULT.
There are 2 solutions:
  #1: ?X=HERU
  #2: ?X=RIDWAN

;;===STOP

and also this one.... (from ";;===START" until ";;===STOP"

;;===START
|= (RETRIEVE ALL (?x) (STUDENT-DEPARTMENT "FTI" ?x))

There are 2 solutions:
  #1: ?X=RIDWAN
  #2: ?X=HERU

;;===STOP

That's the response. Eventhough there're error, but it works.
but after I assert this one, there's something I dont understand. 
Why there's nobody who belong to "FTI" department. "Heru" should
be in "FTI" department, isn't he? There's still default value that
binds him to "FTI" department. (from ";;===START" until ";;===STOP"

;;===START

(assert (STUDENT-DEPARTMENT "FTSP" ridwan))

|= (RETRIEVE ALL (?x) (STUDENT-DEPARTMENT "FTI" ?x))

No solutions.

;;Where is Heru????

|= (RETRIEVE ALL (?x) (STUDENT-DEPARTMENT "FTSP" ?x))

There is 1 solution:
  #1: ?X=RIDWAN

;;===STOP

But After I query one's more, here is the result....(from ";;===START" until
";;===STOP")

;;===START
|= (retrieve (?X) (student-department ?X heru))

Warning: INTERNAL ERROR: DON'T KNOW YET HOW TO EQUATE THINGS BY DEFAULT.
Warning: INTERNAL ERROR: DON'T KNOW YET HOW TO EQUATE THINGS BY DEFAULT.
There is 1 solution so far:
  #1: ?X="FTI"

;;===STOP

Is the way I define the default value, which is

(presume 
	(=> (STUDENT-fti ?STUDENT-fti) 
	    (STUDENT-fti-DEPARTMENT "FTI" ?STUDENT-fti)))

can't be applied to this definition? Or there's a bug in PowerLoom?

Thanx. It is fun to explore the "power" of PowerLoom.

--Ridwan