a-a a-c aaa aac aaf aao aap ac- aca acc acf aco acp af- afa afc aff afo afp aoa aoc aof aoo aop ap- apa apc apf apo app c-- caa cac caf cao cap cca ccc ccf cco ccp cfa cfc cff cfo cfp co- coa coc cof coo cop cpa cpc cpf cpo cpp faa fac faf fao fap fca fcc fcf fco fcp ffa ffc fff ffo ffp foa foc fof foo fop fpa fpc fpo fpp oaa oac oaf oao oap oc- oca occ ocf oco ocp of- ofa ofc off ofo ofp oo- ooa ooc oof ooo oop op- opa opc opf opo opp p-p paa pac paf pao pap pca pcc pcf pco pcp pfa pfc pff pfo pfp poa poc pof poo pop ppa ppc ppf ppo ppp