bbb bbc bbk bbo bbr bbt bcb bcc bck bco bcr bct bkb bkc bkk bko bkr bkt bob boc bok boo bor bot brb brk bro brr brt btb btc btk bto btr btt c-- cbb cbc cbk cbo cbr cbt ccb ccc cck cco ccr cct ckb ckc cko ckt co- cob coc cok coo cor cot crb crc crk cro crr crt ctb ctc ctk cto ctr ctt k-t kbb kbc kbk kbo kbr kcb kcc kck kcr kct kkb kkc kkk kkr kkt kob koc kok koo kor kot krc krk kro krr krt ktb ktc ktk kto ktr ktt ob- obb obc obk obo obr obt oc- ocb occ ock oco ocr oct okb okc okk oko okr oo- oob ooc ook ooo oor oot or- orb orc ork oro orr ort ot- otb otc otk oto otr ott rbb rbc rbk rbo rbr rbt rcb rcc rco rcr rct rkb rkc rkk rko rkt rob roc rok roo ror rot rrb rrc rrk rrr rrt rtb rtc rtk rto rtr rtt tbb tbc tbk tbo tbr tbt tcb tcc tck tco tcr tct tkb tkc tkk tko tkr tkt to- tob toc tok too tor tot trb trc trk tro trr trt ttb ttc ttk tto ttr ttt