a-a a-b a-c aaa aab aac aaf aak aax ab- aba abb abc abf abk abx ac- aca acb acc acf ack acx af- afa afb afc aff afk afx aka akb akc akk ax- axa axk axx baa bab bac baf bak bax bba bbb bbc bbf bbk bbx bca bcb bcc bcf bck bcx bfa bfb bfc bff bfx bka bkb bkc bkf bkk bkx bxb bxx c-- caa cab cac caf cak cax cba cbb cbc cbf cbk cbx cca ccb ccc ccf cck ccx cfa cfb cfc cff cfk cfx cka ckb ckc ckx cxc cxf cxk cxx faa fab fac faf fak fax fba fbb fbc fbf fbk fbx fca fcb fcc fcf fck fcx ffa ffc fff ffk ffx fka fkb fkc fkf fkk fxx ka- kaa kab kac kaf kak kax kba kbb kbc kbf kbk kbx kca kcb kcc kck kcx kfa kfc kff kfx kkb kkc kkk xaa xac xaf xak xbc xbx xcb xcf xcx xfa xfx xkb xxx