a-a a-b aaa aab aao aap aar aas ab- aba abb abo abp abr abs aoa aob aoo aop aor aos ap- apa apb apo app apr aps ar- ara arb aro arp arr ars as- asa asb aso asp asr ass b-p baa bab bao bap bar bas bba bbb bbo bbp bbr bbs boa bob boo bop bor bos bpa bpb bpo bpp bpr bps bra brb bro brp brr brs bsa bsb bso bsp bsr bss oaa oab oao oap oar oas ob- oba obb obo obp obr obs oo- ooa oob ooo oop oor oos op- opa opb opo opp opr ops or- ora orb oro orp orr ors os- osa osb oso osp osr oss p-p paa pab pao pap par pas pba pbb pbo pbp pbr pbs poa pob poo pop por pos ppa ppb ppo ppp ppr pps pra prb pro prp prr prs ps- psa psb pso psp psr pss ra- raa rab rao rap rar ras rba rbb rbo rbp rbr rbs roa rob roo rop ror ros rpa rpb rpo rpp rpr rps rra rrb rrp rrr rrs rsa rsb rso rsp rsr rss saa sab sao sap sar sas sba sbb sbo sbp sbr sbs soa sob soo sop sor sos spa spb spo spp spr sps sr- sra srb sro srp srr srs ss- ssa ssb sso ssp ssr sss