a-a aaa aaf aag aao aas af- afa aff afg afo afs ag- aga agf agg ago ags aoa aof aog aoo aos as- asa asf asg aso ass faa faf fag fao fas ffa fff ffg ffo ffs fga fgf fgg fgs foa fof fog foo fos fsa fsf fsg fso fss gaa gaf gag gao gas gfa gff gfo gfs gga ggg ggo ggs goa gof gog goo gos gsa gsf gsg gso gss oaa oaf oag oao oas of- ofa off ofg ofo ofs oga ogf ogg ogo ogs oo- ooa oof oog ooo oos os- osa osf osg oso oss saa saf sag sao sas sfa sff sfg sfo sfs sga sgf sgg sgo sgs soa sof sog soo sos ss- ssa ssf ssg sso sss