-er bbb bbc bbe bbk bbo bbr bbs bbt bcb bcc bce bck bco bcr bcs bct be- beb bec bee bek beo ber bes bet bkb bkc bke bkk bko bkr bks bkt bob boc boe bok boo bor bos bot brb bre brk bro brr brs brt bsb bsc bse bsk bso bsr bss bst btb btc bte btk bto btr bts btt c-- cbb cbc cbe cbk cbo cbr cbs cbt ccb ccc cce cck cco ccr ccs cct ce- ceb cec cee cek ceo cer ces cet ckb ckc cko cks ckt co- cob coc coe cok coo cor cos cot crb crc cre crk cro crr crs crt csb csc cse csk cso csr css cst ctb ctc cte ctk cto ctr cts ctt ebb ebc ebe ebk ebo ebr ebs ebt ec- ecb ecc ece eck eco ecr ecs ect eeb eec eee eek eeo eer ees eet ekb ekc eke eko ekr eks ekt eo- eob eoc eoe eok eoo eor eos eot erb erc ere erk ero err ers ert es- esb esc ese esk eso esr ess est etb etc ete etk eto etr ets ett k-t kbb kbc kbe kbk kbo kbr kbs kcb kcc kce kck kcr kcs kct ke- keb kec kee kek keo ker kes ket kkb kkc kke kkk kkr kks kkt kob koc koe kok koo kor kos kot krc krk kro krr krs krt ksb ksc kse ksk kso ksr kss kst ktb ktc kte ktk kto ktr kts ktt ob- obb obc obe obk obo obr obs obt oc- ocb occ ock oco ocr ocs oct oeb oec oee oeo oer oes oet okb okc oke okk oko okr oks oo- oob ooc ook ooo oor oos oot or- orb orc ore ork oro orr ors ort os- osb osc ose osk oso osr oss ost ot- otb otc ote otk oto otr ots ott rbb rbc rbe rbk rbo rbr rbs rbt rcb rcc rce rco rcr rcs rct re- reb rec ree rek reo rer res ret rkb rkc rke rkk rko rks rkt rob roc roe rok roo ror ros rot rrb rrc rrk rrr rrs rrt rsb rsc rse rsk rso rsr rss rst rtb rtc rte rtk rto rtr rts rtt sbb sbc sbe sbk sbo sbr sbs sbt scb scc sce sck sco scr scs sct se- seb sec see sek seo ser ses set sk- skb skc ske skk sko skr sks skt sob soc soe sok soo sor sos sot sr- srb src sre srk sro srr srs srt ss- ssb ssc sse ssk sso ssr sss sst stb stc ste stk sto str sts stt tbb tbc tbe tbk tbo tbr tbs tbt tcb tcc tce tck tco tcr tcs tct te- teb tec tee tek teo ter tes tet tkb tkc tke tkk tko tkr tks tkt to- tob toc toe tok too tor tos tot trb trc tre trk tro trr trs trt tsb tsc tse tsk tso tsr tss tst ttb ttc tte ttk tto ttr tts ttt