oo- ooo oop oor oos oot op- opo opp opr ops opt or- oro orp orr ors ort os- oso osp osr oss ost ot- oto otp otr ots ott p-p poo pop por pos pot ppo ppp ppr pps ppt pro prp prr prs prt ps- pso psp psr pss pst pt- pto ptp ptr pts ptt roo rop ror ros rot rpo rpp rpr rps rpt rrp rrr rrs rrt rso rsp rsr rss rst rto rtp rtr rts rtt soo sop sor sos sot spo spp spr sps spt sr- sro srp srr srs srt ss- sso ssp ssr sss sst sto stp str sts stt to- too top tor tos tot tpo tpp tpr tps tpt tro trp trr trs trt tso tsp tsr tss tst tto ttp ttr tts ttt