-er bbb bbc bbe bbk bbn bbo bbr bbs bcb bcc bce bck bcn bco bcr bcs be- beb bec bee bek ben beo ber bes bkb bkc bke bkk bkn bko bkr bks bnb bnc bne bnk bnn bno bnr bns bob boc boe bok bon boo bor bos brb bre brk brn bro brr brs bsb bsc bse bsk bsn bso bsr bss c-- cbb cbc cbe cbk cbn cbo cbr cbs ccb ccc cce cck ccn cco ccr ccs ce- ceb cec cee cek cen ceo cer ces ckb ckc cko cks cn- cnb cnc cne cnn cno cnr cns co- cob coc coe cok con coo cor cos crb crc cre crk crn cro crr crs csb csc cse csk csn cso csr css ebb ebc ebe ebk ebn ebo ebr ebs ec- ecb ecc ece eck ecn eco ecr ecs eeb eec eee eek een eeo eer ees ekb ekc eke eko ekr eks en- enb enc ene enk enn eno enr ens eo- eob eoc eoe eok eon eoo eor eos erb erc ere erk ern ero err ers es- esb esc ese esk esn eso esr ess kbb kbc kbe kbk kbn kbo kbr kbs kcb kcc kce kck kcn kcr kcs ke- keb kec kee kek ken keo ker kes kkb kkc kke kkk kkn kkr kks kn- knc kne knk knn kno knr kob koc koe kok kon koo kor kos krc krk krn kro krr krs ksb ksc kse ksk ksn kso ksr kss nbb nbc nbe nbk nbn nbo nbr nbs ncb ncc nce nck ncn nco ncr ncs ne- neb nec nee nek nen neo ner nes nkc nke nkk nkn nko nkr nks nnb nnc nne nnk nnn nno nns no- nob noc noe nok non noo nor nos nrb nrc nre nrk nrn nro nrr nrs nsb nsc nse nsk nsn nso nsr nss ob- obb obc obe obk obn obo obr obs oc- ocb occ ock ocn oco ocr ocs oeb oec oee oen oeo oer oes okb okc oke okk oko okr oks on- onb onc one onk onn ono onr ons oo- oob ooc ook oon ooo oor oos or- orb orc ore ork orn oro orr ors os- osb osc ose osk osn oso osr oss rbb rbc rbe rbk rbn rbo rbr rbs rcb rcc rce rcn rco rcr rcs re- reb rec ree rek ren reo rer res rkb rkc rke rkk rko rks rnb rnc rnn rno rnr rns rob roc roe rok ron roo ror ros rrb rrc rrk rrn rrr rrs rsb rsc rse rsk rsn rso rsr rss sbb sbc sbe sbk sbn sbo sbr sbs scb scc sce sck scn sco scr scs se- seb sec see sek sen seo ser ses sk- skb skc ske skk sko skr sks snb snc sne snk snn sno snr sns sob soc soe sok son soo sor sos sr- srb src sre srk srn sro srr srs ss- ssb ssc sse ssk ssn sso ssr sss