a-a a-b aaa aab aad aaf aak aao aar ab- aba abb abd abf abk abo abr ad- ada adb add adf adk ado adr af- afa afb afd aff afk afo afr aka akb akd akk ako akr aoa aob aod aof aok aoo aor ar- ara arb ard arf ark aro arr baa bab bad baf bak bao bar bba bbb bbd bbf bbk bbo bbr bda bdb bdd bdf bdk bdo bdr bfa bfb bfd bff bfo bfr bka bkb bkf bkk bko bkr boa bob bod bof bok boo bor bra brb brd brf brk bro brr daa dab dad daf dak dao dar dba dbb dbd dbf dbk dbo dbr dda ddb ddd ddf ddk ddo ddr dfa dfb dfd dff dfk dfo dfr dka dkb dkk dko dkr doa dob dod dof dok doo dor dra drb drd drk dro drr faa fab fad faf fak fao far fba fbb fbd fbf fbk fbo fbr fda fdb fdd fdf fdk fdo fdr ffa ffd fff ffk ffo ffr fka fkb fkf fkk foa fob fof fok foo for fra frb frd frf frk fro frr ka- kaa kab kad kaf kak kao kar kba kbb kbd kbf kbk kbo kbr kda kdb kdf kdk kdo kdr kfa kfd kff kfo kkb kkk kkr koa kob kod kof kok koo kor kra krd krf krk kro krr oaa oab oad oaf oak oao oar ob- oba obb obd obf obk obo obr oda odb odd odf odo odr of- ofa ofb ofd off ofo ofr oka okb okd okk oko okr oo- ooa oob ood oof ook ooo oor or- ora orb ord orf ork oro orr ra- raa rab rad raf rak rao rar rba rbb rbd rbf rbk rbo rbr rda rdb rdd rdf rdo rdr rfa rfb rfd rff rfk rfo rfr rkb rkf rkk rko roa rob rod rof rok roo ror rra rrb rrd rrf rrk rrr