a-a a-b aaa aab aaf aao aap aar aas ab- aba abb abf abo abp abr abs af- afa afb aff afo afp afr afs aoa aob aof aoo aop aor aos ap- apa apb apf apo app apr aps ar- ara arb arf aro arp arr ars as- asa asb asf aso asp asr ass b-p baa bab baf bao bap bar bas bba bbb bbf bbo bbp bbr bbs bfa bfb bff bfo bfp bfr bfs boa bob bof boo bop bor bos bpa bpb bpf bpo bpp bpr bps bra brb brf bro brp brr brs bsa bsb bsf bso bsp bsr bss faa fab faf fao fap far fas fba fbb fbf fbo fbp fbr fbs ffa fff ffo ffp ffr ffs foa fob fof foo fop for fos fpa fpb fpo fpp fpr fps fra frb frf fro frp frr frs fsa fsb fsf fso fsp fsr fss oaa oab oaf oao oap oar oas ob- oba obb obf obo obp obr obs of- ofa ofb off ofo ofp ofr ofs oo- ooa oob oof ooo oop oor oos op- opa opb opf opo opp opr ops or- ora orb orf oro orp orr ors os- osa osb osf oso osp osr oss p-p paa pab paf pao pap par pas pba pbb pbf pbo pbp pbr pbs pfa pfb pff pfo pfp pfr pfs poa pob pof poo pop por pos ppa ppb ppf ppo ppp ppr pps pra prb prf pro prp prr prs ps- psa psb psf pso psp psr pss ra- raa rab raf rao rap rar ras rba rbb rbf rbo rbp rbr rbs rfa rfb rff rfo rfp rfr rfs roa rob rof roo rop ror ros rpa rpb rpf rpo rpp rpr rps rra rrb rrf rrp rrr rrs rsa rsb rsf rso rsp rsr rss saa sab saf sao sap sar sas sba sbb sbf sbo sbp sbr sbs sfa sfb sff sfo sfp sfr sfs soa sob sof soo sop sor sos spa spb spf spo spp spr sps sr- sra srb srf sro srp srr srs ss- ssa ssb ssf sso ssp ssr sss