-er a-a a-b a-c aaa aab aac aae aak aao aar aax ab- aba abb abc abe abk abo abr abx ac- aca acb acc ace ack aco acr acx aea aeb aec aee aek aeo aer aex aka akb akc ake akk ako akr aoa aob aoc aoe aok aoo aor aox ar- ara arb arc are ark aro arr arx ax- axa axe axk axo axr axx baa bab bac bae bak bao bar bax bba bbb bbc bbe bbk bbo bbr bbx bca bcb bcc bce bck bco bcr bcx be- bea beb bec bee bek beo ber bex bka bkb bkc bke bkk bko bkr bkx boa bob boc boe bok boo bor box bra brb bre brk bro brr brx bxb bxo bxx c-- caa cab cac cae cak cao car cax cba cbb cbc cbe cbk cbo cbr cbx cca ccb ccc cce cck cco ccr ccx ce- cea ceb cec cee cek ceo cer cex cka ckb ckc cko ckx co- coa cob coc coe cok coo cor cox cra crb crc cre crk cro crr crx cxc cxk cxo cxr cxx eaa eab eac eae eak eao ear eax eba ebb ebc ebe ebk ebo ebr ebx ec- eca ecb ecc ece eck eco ecr ecx eea eeb eec eee eek eeo eer eex eka ekb ekc eke eko ekr eo- eoa eob eoc eoe eok eoo eor era erb erc ere erk ero err ex- exa exc exe exo exr exx ka- kaa kab kac kae kak kao kar kax kba kbb kbc kbe kbk kbo kbr kbx kca kcb kcc kce kck kcr kcx ke- kea keb kec kee kek keo ker kex kkb kkc kke kkk kkr koa kob koc koe kok koo kor kra krc krk kro krr kxo oaa oab oac oae oak oao oar oax ob- oba obb obc obe obk obo obr obx oc- oca ocb occ ock oco ocr ocx oea oeb oec oee oeo oer oex oka okb okc oke okk oko okr oo- ooa oob ooc ook ooo oor oox or- ora orb orc ore ork oro orr orx ox- oxa oxb oxc oxo oxx ra- raa rab rac rae rak rao rar rax rba rbb rbc rbe rbk rbo rbr rbx rca rcb rcc rce rco rcr rcx re- rea reb rec ree rek reo rer rex rkb rkc rke rkk rko roa rob roc roe rok roo ror rox rra rrb rrc rrk rrr rxr xaa xac xak xar xbc xbe xbr xbx xcb xcr xcx xee xer xex xkb xke xoa xoc xok xoo xor xox xrc xrx xxo xxx