a-a a-b a-c aaa aab aac aad aan ab- aba abb abc abd abn ac- aca acb acc acd acn ad- ada adb adc add adn an- ana anb anc and ann baa bab bac bad ban bba bbb bbc bbd bbn bca bcb bcc bcd bcn bda bdb bdc bdd bna bnb bnc bnd bnn c-- caa cab cac cad can cba cbb cbc cbd cbn cca ccb ccc ccd ccn cda cdb cdc cdd cdn cn- cna cnb cnc cnd cnn daa dab dac dad dan dba dbb dbc dbd dbn dca dcb dcc dcd dcn dda ddb ddc ddd ddn dna dnb dnc dnd dnn naa nab nac nad nan nba nbb nbc nbd nbn nca ncb ncc ncd ncn nda ndb ndc ndd ndn nna nnb nnc nnn