-er b-u bbb bbc bbe bbk bbo bbr bbu bcb bcc bce bck bco bcr bcu be- beb bec bee bek beo ber beu bkb bkc bke bkk bko bkr bob boc boe bok boo bor bou brb bre brk bro brr bru bub buc bue buk buo bur buu c-- cbb cbc cbe cbk cbo cbr cbu ccb ccc cce cck cco ccr ccu ce- ceb cec cee cek ceo cer ceu ckb ckc cko co- cob coc coe cok coo cor cou crb crc cre crk cro crr cru cub cuc cue cuk cuo cur cuu ebb ebc ebe ebk ebo ebr ebu ec- ecb ecc ece eck eco ecr ecu eeb eec eee eek eeo eer ekb ekc eke eko ekr eku eo- eob eoc eoe eok eoo eor eou erb erc ere erk ero err eru eu- eub euc eue eur kbb kbc kbe kbk kbo kbr kbu kcb kcc kce kck kcr kcu ke- keb kec kee kek keo ker kkb kkc kke kkk kkr kku kob koc koe kok koo kor kou krc krk kro krr kru kub kuc kue kuk kur kuu ob- obb obc obe obk obo obr obu oc- ocb occ ock oco ocr ocu oeb oec oee oeo oer okb okc oke okk oko okr oku oo- oob ooc ook ooo oor or- orb orc ore ork oro orr oru ou- ouc oue ouk ouo our rbb rbc rbe rbk rbo rbr rbu rcb rcc rce rco rcr rcu re- reb rec ree rek reo rer reu rkb rkc rke rkk rko rku rob roc roe rok roo ror rou rrb rrc rrk rrr rru rub ruc rue ruk ruo rur ruu ubb ubc ube ubk ubo ubr ubu ucb ucc uce uck uco ucr ucu ueb uec uee uer ukb ukc uke ukk ukr uku uob uoc uoe uok uoo uor ur- urb urc ure urk uro urr uru uuc uue uur uuu