a-a a-b a-c a-z aaa aab aac aao aaz ab- aba abb abc abo abz ac- aca acb acc aco acz aoa aob aoc aoo az- aza azb azo azz baa bab bac bao baz bba bbb bbc bbo bca bcb bcc bco bcz boa bob boc boo boz bza bzo bzz c-- caa cab cac cao caz cba cbb cbc cbo cbz cca ccb ccc cco ccz co- coa cob coc coo coz cz- czc czo oaa oab oac oao ob- oba obb obc obo oc- oca ocb occ oco ocz oo- ooa oob ooc ooo oza ozo ozz zaa zab zac zao zaz zbb zbc zco zo- zoa zob zoc zoo zzz