-er bbb bbc bbe bbk bbo bbr bbx bcb bcc bce bck bco bcr bcx be- beb bec bee bek beo ber bex bkb bkc bke bkk bko bkr bkx bob boc boe bok boo bor box brb bre brk bro brr brx bxb bxo bxx c-- cbb cbc cbe cbk cbo cbr cbx ccb ccc cce cck cco ccr ccx ce- ceb cec cee cek ceo cer cex ckb ckc cko ckx co- cob coc coe cok coo cor cox crb crc cre crk cro crr crx cxc cxk cxo cxr cxx ebb ebc ebe ebk ebo ebr ebx ec- ecb ecc ece eck eco ecr ecx eeb eec eee eek eeo eer eex ekb ekc eke eko ekr eo- eob eoc eoe eok eoo eor erb erc ere erk ero err ex- exc exe exo exr exx kbb kbc kbe kbk kbo kbr kbx kcb kcc kce kck kcr kcx ke- keb kec kee kek keo ker kex kkb kkc kke kkk kkr kob koc koe kok koo kor krc krk kro krr kxo ob- obb obc obe obk obo obr obx oc- ocb occ ock oco ocr ocx oeb oec oee oeo oer oex okb okc oke okk oko okr oo- oob ooc ook ooo oor oox or- orb orc ore ork oro orr orx ox- oxb oxc oxo oxx rbb rbc rbe rbk rbo rbr rbx rcb rcc rce rco rcr rcx re- reb rec ree rek reo rer rex rkb rkc rke rkk rko rob roc roe rok roo ror rox rrb rrc rrk rrr rxr xbc xbe xbr xbx xcb xcr xcx xee xer xex xkb xke xoc xok xoo xor xox xrc xrx xxo xxx