-er bbb bbc bbe bbg bbk bbo bbr bbs bcb bcc bce bcg bck bco bcr bcs be- beb bec bee beg bek beo ber bes bgb bgc bge bgg bgk bgo bgr bgs bkb bkc bke bkg bkk bko bkr bks bob boc boe bog bok boo bor bos brb bre brg brk bro brr brs bsb bsc bse bsg bsk bso bsr bss c-- cbb cbc cbe cbg cbk cbo cbr cbs ccb ccc cce ccg cck cco ccr ccs ce- ceb cec cee ceg cek ceo cer ces cgb cgc cge cgg cgo cgr cgs ckb ckc cko cks co- cob coc coe cog cok coo cor cos crb crc cre crg crk cro crr crs csb csc cse csg csk cso csr css ebb ebc ebe ebg ebk ebo ebr ebs ec- ecb ecc ece ecg eck eco ecr ecs eeb eec eee eeg eek eeo eer ees egb egc ege egg ego egr egs ekb ekc eke ekg eko ekr eks eo- eob eoc eoe eog eok eoo eor eos erb erc ere erg erk ero err ers es- esb esc ese esg esk eso esr ess gbc gbe gbg gbk gbo gbr gbs gcb gcc gce gcg gck gco gcr gcs ge- geb gec gee geg gek geo ger ges ggb ggc ggg ggo ggr ggs gkb gko gks gob goc goe gog gok goo gor gos grb grc gre grg grk gro grr grs gsb gsc gse gsg gsk gso gsr gss kbb kbc kbe kbk kbo kbr kbs kcb kcc kce kcg kck kcr kcs ke- keb kec kee keg kek keo ker kes kgb kgc kgo kgs kkb kkc kke kkk kkr kks kob koc koe kog kok koo kor kos krc krg krk kro krr krs ksb ksc kse ksg ksk kso ksr kss ob- obb obc obe obg obk obo obr obs oc- ocb occ ocg ock oco ocr ocs oeb oec oee oeg oeo oer oes ogc oge ogg ogo ogs okb okc oke okg okk oko okr oks oo- oob ooc oog ook ooo oor oos or- orb orc ore org ork oro orr ors os- osb osc ose osg osk oso osr oss rbb rbc rbe rbg rbk rbo rbr rbs rcb rcc rce rcg rco rcr rcs re- reb rec ree reg rek reo rer res rgb rgc rge rgg rgk rgo rgr rgs rkb rkc rke rkg rkk rko rks rob roc roe rog rok roo ror ros rrb rrc rrg rrk rrr rrs rsb rsc rse rsg rsk rso rsr rss sbb sbc sbe sbg sbk sbo sbr sbs scb scc sce scg sck sco scr scs se- seb sec see seg sek seo ser ses sgb sgc sge sgg sgk sgo sgr sgs sk- skb skc ske skg skk sko skr sks sob soc soe sog sok soo sor sos sr- srb src sre srg srk sro srr srs ss- ssb ssc sse ssg ssk sso ssr sss