-er bbb bbc bbe bbk bbo bbr bbt bcb bcc bce bck bco bcr bct be- beb bec bee bek beo ber bet bkb bkc bke bkk bko bkr bkt bob boc boe bok boo bor bot brb bre brk bro brr brt btb btc bte btk bto btr btt c-- cbb cbc cbe cbk cbo cbr cbt ccb ccc cce cck cco ccr cct ce- ceb cec cee cek ceo cer cet ckb ckc cko ckt co- cob coc coe cok coo cor cot crb crc cre crk cro crr crt ctb ctc cte ctk cto ctr ctt ebb ebc ebe ebk ebo ebr ebt ec- ecb ecc ece eck eco ecr ect eeb eec eee eek eeo eer eet ekb ekc eke eko ekr ekt eo- eob eoc eoe eok eoo eor eot erb erc ere erk ero err ert etb etc ete etk eto etr ett k-t kbb kbc kbe kbk kbo kbr kcb kcc kce kck kcr kct ke- keb kec kee kek keo ker ket kkb kkc kke kkk kkr kkt kob koc koe kok koo kor kot krc krk kro krr krt ktb ktc kte ktk kto ktr ktt ob- obb obc obe obk obo obr obt oc- ocb occ ock oco ocr oct oeb oec oee oeo oer oet okb okc oke okk oko okr oo- oob ooc ook ooo oor oot or- orb orc ore ork oro orr ort ot- otb otc ote otk oto otr ott rbb rbc rbe rbk rbo rbr rbt rcb rcc rce rco rcr rct re- reb rec ree rek reo rer ret rkb rkc rke rkk rko rkt rob roc roe rok roo ror rot rrb rrc rrk rrr rrt rtb rtc rte rtk rto rtr rtt tbb tbc tbe tbk tbo tbr tbt tcb tcc tce tck tco tcr tct te- teb tec tee tek teo ter tet tkb tkc tke tkk tko tkr tkt to- tob toc toe tok too tor tot trb trc tre trk tro trr trt ttb ttc tte ttk tto ttr ttt