-er bbb bbc bbe bbf bbk bbo bbr bcb bcc bce bcf bck bco bcr be- beb bec bee bef bek beo ber bfb bfc bfe bff bfo bfr bkb bkc bke bkf bkk bko bkr bob boc boe bof bok boo bor brb bre brf brk bro brr c-- cbb cbc cbe cbf cbk cbo cbr ccb ccc cce ccf cck cco ccr ce- ceb cec cee cef cek ceo cer cfb cfc cfe cff cfk cfo cfr ckb ckc cko co- cob coc coe cof cok coo cor crb crc cre crf crk cro crr ebb ebc ebe ebf ebk ebo ebr ec- ecb ecc ece ecf eck eco ecr eeb eec eee eef eek eeo eer ef- efb efc efe eff efo efr ekb ekc eke ekf eko ekr eo- eob eoc eoe eof eok eoo eor erb erc ere erf erk ero err fbb fbc fbe fbf fbk fbo fbr fcb fcc fce fcf fck fco fcr feb fec fee fef fek feo fer ffc ffe fff ffk ffo ffr fkb fkc fkf fkk fob foc foe fof fok foo for frb frc fre frf frk fro frr kbb kbc kbe kbf kbk kbo kbr kcb kcc kce kck kcr ke- keb kec kee kef kek keo ker kfc kff kfo kkb kkc kke kkk kkr kob koc koe kof kok koo kor krc krf krk kro krr ob- obb obc obe obf obk obo obr oc- ocb occ ocf ock oco ocr oeb oec oee oef oeo oer of- ofb ofc ofe off ofo ofr okb okc oke okk oko okr oo- oob ooc oof ook ooo oor or- orb orc ore orf ork oro orr rbb rbc rbe rbf rbk rbo rbr rcb rcc rce rcf rco rcr re- reb rec ree ref rek reo rer rfb rfc rfe rff rfk rfo rfr rkb rkc rke rkf rkk rko rob roc roe rof rok roo ror rrb rrc rrf rrk rrr