a-a a-b a-t aaa aab aao aap aar aat ab- aba abb abo abp abr abt aoa aob aoo aop aor aot ap- apa apb apo app apr apt ar- ara arb aro arp arr art at- ata atb ato atp atr att b-p baa bab bao bap bar bat bba bbb bbo bbp bbr bbt boa bob boo bop bor bot bpa bpb bpo bpp bpr bpt bra brb bro brp brr brt bta btb bto btp btr btt oaa oab oao oap oar oat ob- oba obb obo obp obr obt oo- ooa oob ooo oop oor oot op- opa opb opo opp opr opt or- ora orb oro orp orr ort ot- ota otb oto otp otr ott p-p paa pab pao pap par pat pba pbb pbo pbp pbr pbt poa pob poo pop por pot ppa ppb ppo ppp ppr ppt pra prb pro prp prr prt pt- pta ptb pto ptp ptr ptt ra- raa rab rao rap rar rat rba rbb rbo rbp rbr rbt roa rob roo rop ror rot rpa rpb rpo rpp rpr rpt rra rrb rrp rrr rrt rta rtb rto rtp rtr rtt taa tab tao tap tar tat tba tbb tbo tbp tbr tbt to- toa tob too top tor tot tpa tpb tpo tpp tpr tpt tra trb tro trp trr trt tta ttb tto ttp ttr ttt