bbb bbc bbk bbn bbo bcb bcc bck bcn bco bkb bkc bkk bkn bko bnb bnc bnk bnn bno bob boc bok bon boo c-- cbb cbc cbk cbn cbo ccb ccc cck ccn cco ckb ckc cko cn- cnb cnc cnn cno co- cob coc cok con coo kbb kbc kbk kbn kbo kcb kcc kck kcn kkb kkc kkk kkn kn- knc knk knn kno kob koc kok kon koo nbb nbc nbk nbn nbo ncb ncc nck ncn nco nkc nkk nkn nko nnb nnc nnk nnn nno no- nob noc nok non noo ob- obb obc obk obn obo oc- ocb occ ock ocn oco okb okc okk oko on- onb onc onk onn ono oo- oob ooc ook oon ooo