a-a a-b a-c aaa aab aac aae aaf aak aan ab- aba abb abc abe abf abk abn ac- aca acb acc ace acf ack acn aea aeb aec aee aef aek aen af- afa afb afc afe aff afk afn aka akb akc ake akk akn an- ana anb anc ane anf ank ann baa bab bac bae baf bak ban bba bbb bbc bbe bbf bbk bbn bca bcb bcc bce bcf bck bcn be- bea beb bec bee bef bek ben bfa bfb bfc bfe bff bfn bka bkb bkc bke bkf bkk bkn bna bnb bnc bne bnf bnk bnn c-- caa cab cac cae caf cak can cba cbb cbc cbe cbf cbk cbn cca ccb ccc cce ccf cck ccn ce- cea ceb cec cee cef cek cen cfa cfb cfc cfe cff cfk cfn cka ckb ckc cn- cna cnb cnc cne cnf cnn eaa eab eac eae eaf eak ean eba ebb ebc ebe ebf ebk ebn ec- eca ecb ecc ece ecf eck ecn eea eeb eec eee eef eek een ef- efa efb efc efe eff eka ekb ekc eke ekf en- ena enb enc ene enf enk enn faa fab fac fae faf fak fan fba fbb fbc fbe fbf fbk fbn fca fcb fcc fce fcf fck fcn fea feb fec fee fef fek fen ffa ffc ffe fff ffk ffn fka fkb fkc fkf fkk fna fnb fnc fne fnf fnk fnn ka- kaa kab kac kae kaf kak kan kba kbb kbc kbe kbf kbk kbn kca kcb kcc kce kck kcn ke- kea keb kec kee kef kek ken kfa kfc kff kkb kkc kke kkk kkn kn- kna knc kne knf knk knn naa nab nac nae naf nak nan nba nbb nbc nbe nbf nbk nbn nca ncb ncc nce ncf nck ncn ne- nea neb nec nee nef nek nen nfa nfb nfc nfe nff nfk nfn nka nkc nke nkf nkk nkn nna nnb nnc nne nnf nnk nnn