a-a a-c aaa aac aad aaf aao ac- aca acc acd acf aco ad- ada adc add adf ado af- afa afc afd aff afo aoa aoc aod aof aoo c-- caa cac cad caf cao cca ccc ccd ccf cco cda cdc cdd cdf cdo cfa cfc cfd cff cfo co- coa coc cod cof coo daa dac dad daf dao dca dcc dcd dcf dco dda ddc ddd ddf ddo dfa dfc dfd dff dfo doa doc dod dof doo faa fac fad faf fao fca fcc fcd fcf fco fda fdc fdd fdf fdo ffa ffc ffd fff ffo foa foc fof foo oaa oac oad oaf oao oc- oca occ ocd ocf oco oda odc odd odf odo of- ofa ofc ofd off ofo oo- ooa ooc ood oof ooo