a-a a-b a-c a-z aaa aab aac aan aaz ab- aba abb abc abn abz ac- aca acb acc acn acz an- ana anb anc ann anz az- aza azb azn azz baa bab bac ban baz bba bbb bbc bbn bca bcb bcc bcn bcz bna bnb bnc bnn bnz bza bzn bzz c-- caa cab cac can caz cba cbb cbc cbn cbz cca ccb ccc ccn ccz cn- cna cnb cnc cnn cz- czc naa nab nac nan naz nba nbb nbc nbn nca ncb ncc ncn nna nnb nnc nnn nnz nzb nzz zaa zab zac zan zaz zbb zbc znc znn zzz