a-a a-b a-c aaa aab aac aak aao aax ab- aba abb abc abk abo abx ac- aca acb acc ack aco acx aka akb akc akk ako aoa aob aoc aok aoo aox ax- axa axk axo axx baa bab bac bak bao bax bba bbb bbc bbk bbo bbx bca bcb bcc bck bco bcx bka bkb bkc bkk bko bkx boa bob boc bok boo box bxb bxo bxx c-- caa cab cac cak cao cax cba cbb cbc cbk cbo cbx cca ccb ccc cck cco ccx cka ckb ckc cko ckx co- coa cob coc cok coo cox cxc cxk cxo cxx ka- kaa kab kac kak kao kax kba kbb kbc kbk kbo kbx kca kcb kcc kck kcx kkb kkc kkk koa kob koc kok koo kxo oaa oab oac oak oao oax ob- oba obb obc obk obo obx oc- oca ocb occ ock oco ocx oka okb okc okk oko oo- ooa oob ooc ook ooo oox ox- oxa oxb oxc oxo oxx xaa xac xak xbc xbx xcb xcx xkb xoa xoc xok xoo xox xxo xxx