a-a a-b aaa aab aap aar aas ab- aba abb abp abr abs ap- apa apb app apr aps ar- ara arb arp arr ars as- asa asb asp asr ass b-p baa bab bap bar bas bba bbb bbp bbr bbs bpa bpb bpp bpr bps bra brb brp brr brs bsa bsb bsp bsr bss p-p paa pab pap par pas pba pbb pbp pbr pbs ppa ppb ppp ppr pps pra prb prp prr prs ps- psa psb psp psr pss ra- raa rab rap rar ras rba rbb rbp rbr rbs rpa rpb rpp rpr rps rra rrb rrp rrr rrs rsa rsb rsp rsr rss saa sab sap sar sas sba sbb sbp sbr sbs spa spb spp spr sps sr- sra srb srp srr srs ss- ssa ssb ssp ssr sss