-er bbb bbc bbe bbo bbr bbs bcb bcc bce bco bcr bcs be- beb bec bee beo ber bes bob boc boe boo bor bos brb bre bro brr brs bsb bsc bse bso bsr bss c-- cbb cbc cbe cbo cbr cbs ccb ccc cce cco ccr ccs ce- ceb cec cee ceo cer ces co- cob coc coe coo cor cos crb crc cre cro crr crs csb csc cse cso csr css ebb ebc ebe ebo ebr ebs ec- ecb ecc ece eco ecr ecs eeb eec eee eeo eer ees eo- eob eoc eoe eoo eor eos erb erc ere ero err ers es- esb esc ese eso esr ess ob- obb obc obe obo obr obs oc- ocb occ oco ocr ocs oeb oec oee oeo oer oes oo- oob ooc ooo oor oos or- orb orc ore oro orr ors os- osb osc ose oso osr oss rbb rbc rbe rbo rbr rbs rcb rcc rce rco rcr rcs re- reb rec ree reo rer res rob roc roe roo ror ros rrb rrc rrr rrs rsb rsc rse rso rsr rss sbb sbc sbe sbo sbr sbs scb scc sce sco scr scs se- seb sec see seo ser ses sob soc soe soo sor sos sr- srb src sre sro srr srs ss- ssb ssc sse sso ssr sss