-er bbb bbe bbk bbo bbr bbt be- beb bee bek beo ber bet bkb bke bkk bko bkr bkt bob boe bok boo bor bot brb bre brk bro brr brt btb bte btk bto btr btt ebb ebe ebk ebo ebr ebt eeb eee eek eeo eer eet ekb eke eko ekr ekt eo- eob eoe eok eoo eor eot erb ere erk ero err ert etb ete etk eto etr ett k-t kbb kbe kbk kbo kbr ke- keb kee kek keo ker ket kkb kke kkk kkr kkt kob koe kok koo kor kot krk kro krr krt ktb kte ktk kto ktr ktt ob- obb obe obk obo obr obt oeb oee oeo oer oet okb oke okk oko okr oo- oob ook ooo oor oot or- orb ore ork oro orr ort ot- otb ote otk oto otr ott rbb rbe rbk rbo rbr rbt re- reb ree rek reo rer ret rkb rke rkk rko rkt rob roe rok roo ror rot rrb rrk rrr rrt rtb rte rtk rto rtr rtt tbb tbe tbk tbo tbr tbt te- teb tee tek teo ter tet tkb tke tkk tko tkr tkt to- tob toe tok too tor tot trb tre trk tro trr trt ttb tte ttk tto ttr ttt