a-a a-b aaa aab aak aan aao aas ab- aba abb abk abn abo abs aka akb akk akn ako aks an- ana anb ank ann ano ans aoa aob aok aon aoo aos as- asa asb ask asn aso ass baa bab bak ban bao bas bba bbb bbk bbn bbo bbs bka bkb bkk bkn bko bks bna bnb bnk bnn bno bns boa bob bok bon boo bos bsa bsb bsk bsn bso bss ka- kaa kab kak kan kao kas kba kbb kbk kbn kbo kbs kkb kkk kkn kks kn- kna knk knn kno koa kob kok kon koo kos ksa ksb ksk ksn kso kss naa nab nak nan nao nas nba nbb nbk nbn nbo nbs nka nkk nkn nko nks nna nnb nnk nnn nno nns no- noa nob nok non noo nos nsa nsb nsk nsn nso nss oaa oab oak oan oao oas ob- oba obb obk obn obo obs oka okb okk oko oks on- ona onb onk onn ono ons oo- ooa oob ook oon ooo oos os- osa osb osk osn oso oss saa sab sak san sao sas sba sbb sbk sbn sbo sbs sk- ska skb skk sko sks sna snb snk snn sno sns soa sob sok son soo sos ss- ssa ssb ssk ssn sso sss