-er a-a a-b aaa aab aae aaf aak aan aao aar ab- aba abb abe abf abk abn abo abr aea aeb aee aef aek aen aeo aer af- afa afb afe aff afk afn afo afr aka akb ake akk akn ako akr an- ana anb ane anf ank ann ano anr aoa aob aoe aof aok aon aoo aor ar- ara arb are arf ark arn aro arr baa bab bae baf bak ban bao bar bba bbb bbe bbf bbk bbn bbo bbr be- bea beb bee bef bek ben beo ber bfa bfb bfe bff bfn bfo bfr bka bkb bke bkf bkk bkn bko bkr bna bnb bne bnf bnk bnn bno bnr boa bob boe bof bok bon boo bor bra brb bre brf brk brn bro brr eaa eab eae eaf eak ean eao ear eba ebb ebe ebf ebk ebn ebo ebr eea eeb eee eef eek een eeo eer ef- efa efb efe eff efo efr eka ekb eke ekf eko ekr en- ena enb ene enf enk enn eno enr eo- eoa eob eoe eof eok eon eoo eor era erb ere erf erk ern ero err faa fab fae faf fak fan fao far fba fbb fbe fbf fbk fbn fbo fbr fea feb fee fef fek fen feo fer ffa ffe fff ffk ffn ffo ffr fka fkb fkf fkk fna fnb fne fnf fnk fnn fnr foa fob foe fof fok fon foo for fra frb fre frf frk frn fro frr ka- kaa kab kae kaf kak kan kao kar kba kbb kbe kbf kbk kbn kbo kbr ke- kea keb kee kef kek ken keo ker kfa kff kfo kkb kke kkk kkn kkr kn- kna kne knf knk knn kno knr koa kob koe kof kok kon koo kor kra krf krk krn kro krr naa nab nae naf nak nan nao nar nba nbb nbe nbf nbk nbn nbo nbr ne- nea neb nee nef nek nen neo ner nfa nfb nfe nff nfk nfn nfo nfr nka nke nkf nkk nkn nko nkr nna nnb nne nnf nnk nnn nno no- noa nob noe nof nok non noo nor nra nrb nre nrf nrk nrn nro nrr oaa oab oae oaf oak oan oao oar ob- oba obb obe obf obk obn obo obr oea oeb oee oef oen oeo oer of- ofa ofb ofe off ofn ofo ofr oka okb oke okk oko okr on- ona onb one onf onk onn ono onr oo- ooa oob oof ook oon ooo oor or- ora orb ore orf ork orn oro orr ra- raa rab rae raf rak ran rao rar rba rbb rbe rbf rbk rbn rbo rbr re- rea reb ree ref rek ren reo rer rfa rfb rfe rff rfk rfn rfo rfr rkb rke rkf rkk rko rna rnb rnn rno rnr roa rob roe rof rok ron roo ror rra rrb rrf rrk rrn rrr