-er bbb bbc bbe bbk bbr bbt bcb bcc bce bck bcr bct be- beb bec bee bek ber bet bkb bkc bke bkk bkr bkt brb bre brk brr brt btb btc bte btk btr btt c-- cbb cbc cbe cbk cbr cbt ccb ccc cce cck ccr cct ce- ceb cec cee cek cer cet ckb ckc ckt crb crc cre crk crr crt ctb ctc cte ctk ctr ctt ebb ebc ebe ebk ebr ebt ec- ecb ecc ece eck ecr ect eeb eec eee eek eer eet ekb ekc eke ekr ekt erb erc ere erk err ert etb etc ete etk etr ett k-t kbb kbc kbe kbk kbr kcb kcc kce kck kcr kct ke- keb kec kee kek ker ket kkb kkc kke kkk kkr kkt krc krk krr krt ktb ktc kte ktk ktr ktt rbb rbc rbe rbk rbr rbt rcb rcc rce rcr rct re- reb rec ree rek rer ret rkb rkc rke rkk rkt rrb rrc rrk rrr rrt rtb rtc rte rtk rtr rtt tbb tbc tbe tbk tbr tbt tcb tcc tce tck tcr tct te- teb tec tee tek ter tet tkb tkc tke tkk tkr tkt trb trc tre trk trr trt ttb ttc tte ttk ttr ttt