a-a a-c aaa aac aad aaf aan ac- aca acc acd acf acn ad- ada adc add adf adn af- afa afc afd aff afn an- ana anc and anf ann c-- caa cac cad caf can cca ccc ccd ccf ccn cda cdc cdd cdf cdn cfa cfc cfd cff cfn cn- cna cnc cnd cnf cnn daa dac dad daf dan dca dcc dcd dcf dcn dda ddc ddd ddf ddn dfa dfc dfd dff dfn dna dnc dnd dnf dnn faa fac fad faf fan fca fcc fcd fcf fcn fda fdc fdd fdf fdn ffa ffc ffd fff ffn fna fnc fnd fnf fnn naa nac nad naf nan nca ncc ncd ncf ncn nda ndc ndd ndf ndn nfa nfc nfd nff nfn nna nnc nnf nnn