b-p bbb bbo bbp bbr bbt bob boo bop bor bot bpb bpo bpp bpr bpt brb bro brp brr brt btb bto btp btr btt ob- obb obo obp obr obt oo- oob ooo oop oor oot op- opb opo opp opr opt or- orb oro orp orr ort ot- otb oto otp otr ott p-p pbb pbo pbp pbr pbt pob poo pop por pot ppb ppo ppp ppr ppt prb pro prp prr prt pt- ptb pto ptp ptr ptt rbb rbo rbp rbr rbt rob roo rop ror rot rpb rpo rpp rpr rpt rrb rrp rrr rrt rtb rto rtp rtr rtt tbb tbo tbp tbr tbt to- tob too top tor tot tpb tpo tpp tpr tpt trb tro trp trr trt ttb tto ttp ttr ttt