a-a a-b a-c aaa aab aac aae aan ab- aba abb abc abe abn ac- aca acb acc ace acn aea aeb aec aee aen an- ana anb anc ane ann baa bab bac bae ban bba bbb bbc bbe bbn bca bcb bcc bce bcn be- bea beb bec bee ben bna bnb bnc bne bnn c-- caa cab cac cae can cba cbb cbc cbe cbn cca ccb ccc cce ccn ce- cea ceb cec cee cen cn- cna cnb cnc cne cnn eaa eab eac eae ean eba ebb ebc ebe ebn ec- eca ecb ecc ece ecn eea eeb eec eee een en- ena enb enc ene enn naa nab nac nae nan nba nbb nbc nbe nbn nca ncb ncc nce ncn ne- nea neb nec nee nen nna nnb nnc nne nnn