-er a-a a-b a-c aaa aab aac aae aaf aak aao aar ab- aba abb abc abe abf abk abo abr ac- aca acb acc ace acf ack aco acr aea aeb aec aee aef aek aeo aer af- afa afb afc afe aff afk afo afr aka akb akc ake akk ako akr aoa aob aoc aoe aof aok aoo aor ar- ara arb arc are arf ark aro arr baa bab bac bae baf bak bao bar bba bbb bbc bbe bbf bbk bbo bbr bca bcb bcc bce bcf bck bco bcr be- bea beb bec bee bef bek beo ber bfa bfb bfc bfe bff bfo bfr bka bkb bkc bke bkf bkk bko bkr boa bob boc boe bof bok boo bor bra brb bre brf brk bro brr c-- caa cab cac cae caf cak cao car cba cbb cbc cbe cbf cbk cbo cbr cca ccb ccc cce ccf cck cco ccr ce- cea ceb cec cee cef cek ceo cer cfa cfb cfc cfe cff cfk cfo cfr cka ckb ckc cko co- coa cob coc coe cof cok coo cor cra crb crc cre crf crk cro crr eaa eab eac eae eaf eak eao ear eba ebb ebc ebe ebf ebk ebo ebr ec- eca ecb ecc ece ecf eck eco ecr eea eeb eec eee eef eek eeo eer ef- efa efb efc efe eff efo efr eka ekb ekc eke ekf eko ekr eo- eoa eob eoc eoe eof eok eoo eor era erb erc ere erf erk ero err faa fab fac fae faf fak fao far fba fbb fbc fbe fbf fbk fbo fbr fca fcb fcc fce fcf fck fco fcr fea feb fec fee fef fek feo fer ffa ffc ffe fff ffk ffo ffr fka fkb fkc fkf fkk foa fob foc foe fof fok foo for fra frb frc fre frf frk fro frr ka- kaa kab kac kae kaf kak kao kar kba kbb kbc kbe kbf kbk kbo kbr kca kcb kcc kce kck kcr ke- kea keb kec kee kef kek keo ker kfa kfc kff kfo kkb kkc kke kkk kkr koa kob koc koe kof kok koo kor kra krc krf krk kro krr oaa oab oac oae oaf oak oao oar ob- oba obb obc obe obf obk obo obr oc- oca ocb occ ocf ock oco ocr oea oeb oec oee oef oeo oer of- ofa ofb ofc ofe off ofo ofr oka okb okc oke okk oko okr oo- ooa oob ooc oof ook ooo oor or- ora orb orc ore orf ork oro orr ra- raa rab rac rae raf rak rao rar rba rbb rbc rbe rbf rbk rbo rbr rca rcb rcc rce rcf rco rcr re- rea reb rec ree ref rek reo rer rfa rfb rfc rfe rff rfk rfo rfr rkb rkc rke rkf rkk rko roa rob roc roe rof rok roo ror rra rrb rrc rrf rrk rrr