-er bbb bbc bbe bbk bbo bbr bcb bcc bce bck bco bcr be- beb bec bee bek beo ber bkb bkc bke bkk bko bkr bob boc boe bok boo bor brb bre brk bro brr c-- cbb cbc cbe cbk cbo cbr ccb ccc cce cck cco ccr ce- ceb cec cee cek ceo cer ckb ckc cko co- cob coc coe cok coo cor crb crc cre crk cro crr ebb ebc ebe ebk ebo ebr ec- ecb ecc ece eck eco ecr eeb eec eee eek eeo eer ekb ekc eke eko ekr eo- eob eoc eoe eok eoo eor erb erc ere erk ero err kbb kbc kbe kbk kbo kbr kcb kcc kce kck kcr ke- keb kec kee kek keo ker kkb kkc kke kkk kkr kob koc koe kok koo kor krc krk kro krr ob- obb obc obe obk obo obr oc- ocb occ ock oco ocr oeb oec oee oeo oer okb okc oke okk oko okr oo- oob ooc ook ooo oor or- orb orc ore ork oro orr rbb rbc rbe rbk rbo rbr rcb rcc rce rco rcr re- reb rec ree rek reo rer rkb rkc rke rkk rko rob roc roe rok roo ror rrb rrc rrk rrr