a-a a-b a-t aaa aab aao aar aas aat ab- aba abb abo abr abs abt aoa aob aoo aor aos aot ar- ara arb aro arr ars art as- asa asb aso asr ass ast at- ata atb ato atr ats att baa bab bao bar bas bat bba bbb bbo bbr bbs bbt boa bob boo bor bos bot bra brb bro brr brs brt bsa bsb bso bsr bss bst bta btb bto btr bts btt oaa oab oao oar oas oat ob- oba obb obo obr obs obt oo- ooa oob ooo oor oos oot or- ora orb oro orr ors ort os- osa osb oso osr oss ost ot- ota otb oto otr ots ott ra- raa rab rao rar ras rat rba rbb rbo rbr rbs rbt roa rob roo ror ros rot rra rrb rrr rrs rrt rsa rsb rso rsr rss rst rta rtb rto rtr rts rtt saa sab sao sar sas sat sba sbb sbo sbr sbs sbt soa sob soo sor sos sot sr- sra srb sro srr srs srt ss- ssa ssb sso ssr sss sst sta stb sto str sts stt taa tab tao tar tas tat tba tbb tbo tbr tbs tbt to- toa tob too tor tos tot tra trb tro trr trs trt tsa tsb tso tsr tss tst tta ttb tto ttr tts ttt