b-p bbb bbo bbp bbr bbs bob boo bop bor bos bpb bpo bpp bpr bps brb bro brp brr brs bsb bso bsp bsr bss ob- obb obo obp obr obs oo- oob ooo oop oor oos op- opb opo opp opr ops or- orb oro orp orr ors os- osb oso osp osr oss p-p pbb pbo pbp pbr pbs pob poo pop por pos ppb ppo ppp ppr pps prb pro prp prr prs ps- psb pso psp psr pss rbb rbo rbp rbr rbs rob roo rop ror ros rpb rpo rpp rpr rps rrb rrp rrr rrs rsb rso rsp rsr rss sbb sbo sbp sbr sbs sob soo sop sor sos spb spo spp spr sps sr- srb sro srp srr srs ss- ssb sso ssp ssr sss