a-a a-b aaa aab aad aak aao aas ab- aba abb abd abk abo abs ad- ada adb add adk ado ads aka akb akd akk ako aks aoa aob aod aok aoo aos as- asa asb asd ask aso ass baa bab bad bak bao bas bba bbb bbd bbk bbo bbs bda bdb bdd bdk bdo bds bka bkb bkk bko bks boa bob bod bok boo bos bsa bsb bsd bsk bso bss daa dab dad dak dao das dba dbb dbd dbk dbo dbs dda ddb ddd ddk ddo dds dka dkb dkk dko dks doa dob dod dok doo dos dsa dsb dsd dsk dso dss ka- kaa kab kad kak kao kas kba kbb kbd kbk kbo kbs kda kdb kdk kdo kds kkb kkk kks koa kob kod kok koo kos ksa ksb ksd ksk kso kss oaa oab oad oak oao oas ob- oba obb obd obk obo obs oda odb odd odo ods oka okb okd okk oko oks oo- ooa oob ood ook ooo oos os- osa osb osd osk oso oss saa sab sad sak sao sas sba sbb sbd sbk sbo sbs sda sdb sdd sdk sdo sds sk- ska skb skd skk sko sks soa sob sod sok soo sos ss- ssa ssb ssd ssk sso sss