;;; added as answer to exercise 5.1.1 - 4
sign := *top* & 
[ ORTH *diff-list*,
  HEAD pos,
  SPR *list*,
  COMPS *list* ].

;;; modified as answer to exercise 5.1.1 - 5
pos := *top* &
[NUMAGR agr].

noun := pos.
verb := pos.
det := pos.
;;; added as answer to exercise 5.1.1 - 2
prep := pos.

;;; added as answer to exercise 5.1.1 - 5
agr := *top*.
;;; added as answer to exercise 5.1.1 - 5
sg := agr.
;;; added as answer to exercise 5.1.1 - 5
pl := agr.

phrase := sign &
[ ARGS *list*].

unary-phrase := phrase &
[ ORTH #orth,
  ARGS [  FIRST [ ORTH #orth]]].

binary-phrase := phrase &
[ ORTH [ LIST #first,
	 LAST #last ],
  ARGS [  FIRST [ ORTH [ LIST #first,
                         LAST #middle ] ], 
          REST [ FIRST [ ORTH [ LIST #middle,
                                LAST #last ]]]]].

ternary-phrase := phrase &
[ ORTH [ LIST #first,
	 LAST #last ],
  ARGS [  FIRST [ ORTH [ LIST #first,
                         LAST #middle1 ] ], 
          REST [ FIRST [ ORTH [ LIST #middle1,
                                LAST #middle2 ]],
          	 REST [ FIRST [ ORTH [ 	LIST #middle2,
                                	LAST #last ]]]]]].

word := sign &
[ ORTH [ LIST [ FIRST string,
                REST #end ],
         LAST #end ]].

;;; added as answer to exercise 5.1.1 - 5
sg-word := word &
[ HEAD [ NUMAGR sg ]].

;;; added as answer to exercise 5.1.1 - 5
pl-word := word &
[ HEAD [ NUMAGR pl ]].

;;;;;;;;;;;;;;;;;;;;;;;

string := *top*.

*list* := *top*.

*ne-list* := *list* &
 [ FIRST *top*,
   REST *list* ].

*null* := *list*.

*diff-list* := *top* &
 [ LIST *list*,
   LAST *list* ].