-er a-a a-b a-c aaa aab aac aae aak aao aar ab- aba abb abc abe abk abo abr ac- aca acb acc ace ack aco acr aea aeb aec aee aek aeo aer aka akb akc ake akk ako akr aoa aob aoc aoe aok aoo aor ar- ara arb arc are ark aro arr baa bab bac bae bak bao bar bba bbb bbc bbe bbk bbo bbr bca bcb bcc bce bck bco bcr be- bea beb bec bee bek beo ber bka bkb bkc bke bkk bko bkr boa bob boc boe bok boo bor bra brb bre brk bro brr c-- caa cab cac cae cak cao car cba cbb cbc cbe cbk cbo cbr cca ccb ccc cce cck cco ccr ce- cea ceb cec cee cek ceo cer cka ckb ckc cko co- coa cob coc coe cok coo cor cra crb crc cre crk cro crr eaa eab eac eae eak eao ear eba ebb ebc ebe ebk ebo ebr ec- eca ecb ecc ece eck eco ecr eea eeb eec eee eek eeo eer eka ekb ekc eke eko ekr eo- eoa eob eoc eoe eok eoo eor era erb erc ere erk ero err ka- kaa kab kac kae kak kao kar kba kbb kbc kbe kbk kbo kbr kca kcb kcc kce kck kcr ke- kea keb kec kee kek keo ker kkb kkc kke kkk kkr koa kob koc koe kok koo kor kra krc krk kro krr oaa oab oac oae oak oao oar ob- oba obb obc obe obk obo obr oc- oca ocb occ ock oco ocr oea oeb oec oee oeo oer oka okb okc oke okk oko okr oo- ooa oob ooc ook ooo oor or- ora orb orc ore ork oro orr ra- raa rab rac rae rak rao rar rba rbb rbc rbe rbk rbo rbr rca rcb rcc rce rco rcr re- rea reb rec ree rek reo rer rkb rkc rke rkk rko roa rob roc roe rok roo ror rra rrb rrc rrk rrr