-er a-a a-b aaa aab aae aak aao aar ab- aba abb abe abk abo abr aea aeb aee aek aeo aer aka akb ake akk ako akr aoa aob aoe aok aoo aor ar- ara arb are ark aro arr baa bab bae bak bao bar bba bbb bbe bbk bbo bbr be- bea beb bee bek beo ber bka bkb bke bkk bko bkr boa bob boe bok boo bor bra brb bre brk bro brr eaa eab eae eak eao ear eba ebb ebe ebk ebo ebr eea eeb eee eek eeo eer eka ekb eke eko ekr eo- eoa eob eoe eok eoo eor era erb ere erk ero err ka- kaa kab kae kak kao kar kba kbb kbe kbk kbo kbr ke- kea keb kee kek keo ker kkb kke kkk kkr koa kob koe kok koo kor kra krk kro krr oaa oab oae oak oao oar ob- oba obb obe obk obo obr oea oeb oee oeo oer oka okb oke okk oko okr oo- ooa oob ook ooo oor or- ora orb ore ork oro orr ra- raa rab rae rak rao rar rba rbb rbe rbk rbo rbr re- rea reb ree rek reo rer rkb rke rkk rko roa rob roe rok roo ror rra rrb rrk rrr