a-a aaa aaf aao aap aas af- afa aff afo afp afs aoa aof aoo aop aos ap- apa apf apo app aps as- asa asf aso asp ass faa faf fao fap fas ffa fff ffo ffp ffs foa fof foo fop fos fpa fpo fpp fps fsa fsf fso fsp fss oaa oaf oao oap oas of- ofa off ofo ofp ofs oo- ooa oof ooo oop oos op- opa opf opo opp ops os- osa osf oso osp oss p-p paa paf pao pap pas pfa pff pfo pfp pfs poa pof poo pop pos ppa ppf ppo ppp pps ps- psa psf pso psp pss saa saf sao sap sas sfa sff sfo sfp sfs soa sof soo sop sos spa spf spo spp sps ss- ssa ssf sso ssp sss