fff ffo ffs fft ffy fof foo fos fot foy fsf fso fss fst ftf fto fts ftt fty fy- fyo of- off ofo ofs oft oo- oof ooo oos oot os- osf oso oss ost ot- otf oto ots ott oyo oys sff sfo sfs sft sof soo sos sot soy ss- ssf sso sss sst stf sto sts stt sty sy- sys syt tff tfo tfs tft to- tof too tos tot toy tsf tso tss tst tsy ttf tto tts ttt tty tyf tyo tys tyt yff yfs yft yof yoo yos yot yoy yso yss yst ysy ytf yto yts ytt yyf yys yyt yyy