a-a a-b a-t aaa aab aao aar aas aat aax ab- aba abb abo abr abs abt abx aoa aob aoo aor aos aot aox ar- ara arb aro arr ars art arx as- asa asb aso asr ass ast asx at- ata atb ato atr ats att atx ax- axa axo axr axs axt axx baa bab bao bar bas bat bax bba bbb bbo bbr bbs bbt bbx boa bob boo bor bos bot box bra brb bro brr brs brt brx bsa bsb bso bsr bss bst bsx bta btb bto btr bts btt btx bxb bxo bxx oaa oab oao oar oas oat oax ob- oba obb obo obr obs obt obx oo- ooa oob ooo oor oos oot oox or- ora orb oro orr ors ort orx os- osa osb oso osr oss ost osx ot- ota otb oto otr ots ott ox- oxa oxb oxo oxt oxx ra- raa rab rao rar ras rat rax rba rbb rbo rbr rbs rbt rbx roa rob roo ror ros rot rox rra rrb rrr rrs rrt rsa rsb rso rsr rss rst rsx rta rtb rto rtr rts rtt rtx rxr rxs saa sab sao sar sas sat sax sba sbb sbo sbr sbs sbt sbx soa sob soo sor sos sot sox sr- sra srb sro srr srs srt srx ss- ssa ssb sso ssr sss sst ssx sta stb sto str sts stt stx sxs sxt t-x taa tab tao tar tas tat tax tba tbb tbo tbr tbs tbt to- toa tob too tor tos tot tox tra trb tro trr trs trt trx tsa tsb tso tsr tss tst tsx tta ttb tto ttr tts ttt ttx txs txt xaa xar xas xat xbr xbx xoa xoo xor xos xot xox xrt xrx xsa xsb xss xst xtr xts xtx xxo xxx