a-a a-b a-c aaa aab aac aak aan ab- aba abb abc abk abn ac- aca acb acc ack acn aka akb akc akk akn an- ana anb anc ank ann baa bab bac bak ban bba bbb bbc bbk bbn bca bcb bcc bck bcn bka bkb bkc bkk bkn bna bnb bnc bnk bnn c-- caa cab cac cak can cba cbb cbc cbk cbn cca ccb ccc cck ccn cka ckb ckc cn- cna cnb cnc cnn ka- kaa kab kac kak kan kba kbb kbc kbk kbn kca kcb kcc kck kcn kkb kkc kkk kkn kn- kna knc knk knn naa nab nac nak nan nba nbb nbc nbk nbn nca ncb ncc nck ncn nka nkc nkk nkn nna nnb nnc nnk nnn