a-a a-b aaa aab aad aak aao ab- aba abb abd abk abo ad- ada adb add adk ado aka akb akd akk ako aoa aob aod aok aoo baa bab bad bak bao bba bbb bbd bbk bbo bda bdb bdd bdk bdo bka bkb bkk bko boa bob bod bok boo daa dab dad dak dao dba dbb dbd dbk dbo dda ddb ddd ddk ddo dka dkb dkk dko doa dob dod dok doo ka- kaa kab kad kak kao kba kbb kbd kbk kbo kda kdb kdk kdo kkb kkk koa kob kod kok koo oaa oab oad oak oao ob- oba obb obd obk obo oda odb odd odo oka okb okd okk oko oo- ooa oob ood ook ooo