fff ffo ffr ffs fft ffx fof foo for fos fot fox frf fro frr frs frt fsf fso fsr fss fst fsx ftf fto ftr fts ftt ftx fxr fxs fxt fxx of- off ofo ofr ofs oft ofx oo- oof ooo oor oos oot oox or- orf oro orr ors ort orx os- osf oso osr oss ost osx ot- otf oto otr ots ott ox- oxf oxo oxt oxx rff rfo rfr rfs rft rof roo ror ros rot rox rrf rrr rrs rrt rsf rso rsr rss rst rsx rtf rto rtr rts rtt rtx rxr rxs sff sfo sfr sfs sft sfx sof soo sor sos sot sox sr- srf sro srr srs srt srx ss- ssf sso ssr sss sst ssx stf sto str sts stt stx sxs sxt t-x tff tfo tfr tfs tft tfx to- tof too tor tos tot tox trf tro trr trs trt trx tsf tso tsr tss tst tsx ttf tto ttr tts ttt ttx txf txs txt xfs xft xfx xof xoo xor xos xot xox xrf xrt xrx xss xst xtf xtr xts xtx xxo xxx