oo- ooo oop oor oos oot oox op- opo opp opr ops opt opx or- oro orp orr ors ort orx os- oso osp osr oss ost osx ot- oto otp otr ots ott ox- oxo oxt oxx p-p poo pop por pos pot pox ppo ppp ppr pps ppt ppx pro prp prr prs prt prx ps- pso psp psr pss pst psx pt- pto ptp ptr pts ptt ptx pxr pxs pxt roo rop ror ros rot rox rpo rpp rpr rps rpt rpx rrp rrr rrs rrt rso rsp rsr rss rst rsx rto rtp rtr rts rtt rtx rxp rxr rxs soo sop sor sos sot sox spo spp spr sps spt spx sr- sro srp srr srs srt srx ss- sso ssp ssr sss sst ssx sto stp str sts stt stx sxs sxt t-x to- too top tor tos tot tox tpo tpp tpr tps tpt tpx tro trp trr trs trt trx tso tsp tsr tss tst tsx tto ttp ttr tts ttt ttx txs txt xoo xop xor xos xot xox xpo xpp xps xpt xrt xrx xsp xss xst xtp xtr xts xtx xxo xxp xxx