a-a a-b a-c aaa aab aac aao aax ab- aba abb abc abo abx ac- aca acb acc aco acx aoa aob aoc aoo aox ax- axa axo axx baa bab bac bao bax bba bbb bbc bbo bbx bca bcb bcc bco bcx boa bob boc boo box bxb bxo bxx c-- caa cab cac cao cax cba cbb cbc cbo cbx cca ccb ccc cco ccx co- coa cob coc coo cox cxc cxo cxx oaa oab oac oao oax ob- oba obb obc obo obx oc- oca ocb occ oco ocx oo- ooa oob ooc ooo oox ox- oxa oxb oxc oxo oxx xaa xac xbc xbx xcb xcx xoa xoc xoo xox xxo xxx