-er bbb bbc bbe bbk bbr bcb bcc bce bck bcr be- beb bec bee bek ber bkb bkc bke bkk bkr brb bre brk brr c-- cbb cbc cbe cbk cbr ccb ccc cce cck ccr ce- ceb cec cee cek cer ckb ckc crb crc cre crk crr ebb ebc ebe ebk ebr ec- ecb ecc ece eck ecr eeb eec eee eek eer ekb ekc eke ekr erb erc ere erk err kbb kbc kbe kbk kbr kcb kcc kce kck kcr ke- keb kec kee kek ker kkb kkc kke kkk kkr krc krk krr rbb rbc rbe rbk rbr rcb rcc rce rcr re- reb rec ree rek rer rkb rkc rke rkk rrb rrc rrk rrr