a-a a-b a-c aaa aab aac aae aaf aan ab- aba abb abc abe abf abn ac- aca acb acc ace acf acn aea aeb aec aee aef aen af- afa afb afc afe aff afn an- ana anb anc ane anf ann baa bab bac bae baf ban bba bbb bbc bbe bbf bbn bca bcb bcc bce bcf bcn be- bea beb bec bee bef ben bfa bfb bfc bfe bff bfn bna bnb bnc bne bnf bnn c-- caa cab cac cae caf can cba cbb cbc cbe cbf cbn cca ccb ccc cce ccf ccn ce- cea ceb cec cee cef cen cfa cfb cfc cfe cff cfn cn- cna cnb cnc cne cnf cnn eaa eab eac eae eaf ean eba ebb ebc ebe ebf ebn ec- eca ecb ecc ece ecf ecn eea eeb eec eee eef een ef- efa efb efc efe eff en- ena enb enc ene enf enn faa fab fac fae faf fan fba fbb fbc fbe fbf fbn fca fcb fcc fce fcf fcn fea feb fec fee fef fen ffa ffc ffe fff ffn fna fnb fnc fne fnf fnn naa nab nac nae naf nan nba nbb nbc nbe nbf nbn nca ncb ncc nce ncf ncn ne- nea neb nec nee nef nen nfa nfb nfc nfe nff nfn nna nnb nnc nne nnf nnn