a-a a-b a-t aaa aab aap aar aat ab- aba abb abp abr abt ap- apa apb app apr apt ar- ara arb arp arr art at- ata atb atp atr att b-p baa bab bap bar bat bba bbb bbp bbr bbt bpa bpb bpp bpr bpt bra brb brp brr brt bta btb btp btr btt p-p paa pab pap par pat pba pbb pbp pbr pbt ppa ppb ppp ppr ppt pra prb prp prr prt pt- pta ptb ptp ptr ptt ra- raa rab rap rar rat rba rbb rbp rbr rbt rpa rpb rpp rpr rpt rra rrb rrp rrr rrt rta rtb rtp rtr rtt taa tab tap tar tat tba tbb tbp tbr tbt tpa tpb tpp tpr tpt tra trb trp trr trt tta ttb ttp ttr ttt