(loop
		for wall = (generate-wall walls paths)
		when (> counter 3)
		  do (return)
		if (loop named internal-loop ;all paths exist
				 for hex1 in hexes
				 while (loop for hex2 in hexes
							 unless (path-exists-p hex1 hex2 (remove wall paths :test #'connection-equal-p))
							   do (return-from internal-loop nil)
							 finally (return-from internal-loop t)))
		   (update-with-wall walls paths wall)
		else
		(setf counter (1+ counter)))

; caught ERROR:
;   during macroexpansion of (LOOP FOR WALL ...). Use *BREAK-ON-SIGNALS* to
;   intercept.
;   
;    (UPDATE-WITH-WALL WALLS PATHS
;                      WALL) found where keyword expected getting LOOP clause after IF
;   current LOOP context: IF (LOOP NAMED INTERNAL-LOOP
;                                  FOR HEX1 IN HEXES
;                                  WHILE (LOOP FOR HEX2 IN HEXES
;                                              UNLESS (PATH-EXISTS-P HEX1 HEX2
;                                                                    (REMOVE WALL
;                                                                            PATHS
;                                                                            :TEST
;                                                                            #'CONNECTION-EQUAL-P))
;                                              DO (RETURN-FROM INTERNAL-LOOP NIL)
;                                              FINALLY (RETURN-FROM INTERNAL-LOOP
;                                                        T))) (UPDATE-WITH-WALL
;                                                              WALLS PATHS WALL).
; 
; compilation unit finished
;   caught 1 ERROR condition