-er bbb bbc bbe bbk bbr bbs bcb bcc bce bck bcr bcs be- beb bec bee bek ber bes bkb bkc bke bkk bkr bks brb bre brk brr brs bsb bsc bse bsk bsr bss c-- cbb cbc cbe cbk cbr cbs ccb ccc cce cck ccr ccs ce- ceb cec cee cek cer ces ckb ckc cks crb crc cre crk crr crs csb csc cse csk csr css ebb ebc ebe ebk ebr ebs ec- ecb ecc ece eck ecr ecs eeb eec eee eek eer ees ekb ekc eke ekr eks erb erc ere erk err ers es- esb esc ese esk esr ess kbb kbc kbe kbk kbr kbs kcb kcc kce kck kcr kcs ke- keb kec kee kek ker kes kkb kkc kke kkk kkr kks krc krk krr krs ksb ksc kse ksk ksr kss rbb rbc rbe rbk rbr rbs rcb rcc rce rcr rcs re- reb rec ree rek rer res rkb rkc rke rkk rks rrb rrc rrk rrr rrs rsb rsc rse rsk rsr rss sbb sbc sbe sbk sbr sbs scb scc sce sck scr scs se- seb sec see sek ser ses sk- skb skc ske skk skr sks sr- srb src sre srk srr srs ss- ssb ssc sse ssk ssr sss