a-a a-b aaa aab aaf aak aan ab- aba abb abf abk abn af- afa afb aff afk afn aka akb akk akn an- ana anb anf ank ann baa bab baf bak ban bba bbb bbf bbk bbn bfa bfb bff bfn bka bkb bkf bkk bkn bna bnb bnf bnk bnn faa fab faf fak fan fba fbb fbf fbk fbn ffa fff ffk ffn fka fkb fkf fkk fna fnb fnf fnk fnn ka- kaa kab kaf kak kan kba kbb kbf kbk kbn kfa kff kkb kkk kkn kn- kna knf knk knn naa nab naf nak nan nba nbb nbf nbk nbn nfa nfb nff nfk nfn nka nkf nkk nkn nna nnb nnf nnk nnn