bf front_camera
bf back_camera
bf touch_screen
bf basic_screen
bf keypad
bf calling_feature
bf mp3
bf gps
bf battery
( = camera ( some_of front_camera back_camera ) )
( = screen ( one_of touch_screen basic_screen ) )
( = acessories ( some_of gps camera mp3 ) )
( = batteries ( ^ battery 1..2 ) )
( = mobile ( all_of screen calling_feature ( opt keypad ) ( opt acessories ) batteries ) )
( mobile exclude touch_screen keypad )
{( refine mobile batteries ),
( mobile every_family_has gps  )
,
}
