a-a a-b a-t aaa aab aar aas aat aax ab- aba abb abr abs abt abx ar- ara arb arr ars art arx as- asa asb asr ass ast asx at- ata atb atr ats att atx ax- axa axr axs axt axx baa bab bar bas bat bax bba bbb bbr bbs bbt bbx bra brb brr brs brt brx bsa bsb bsr bss bst bsx bta btb btr bts btt btx bxb bxx ra- raa rab rar ras rat rax rba rbb rbr rbs rbt rbx rra rrb rrr rrs rrt rsa rsb rsr rss rst rsx rta rtb rtr rts rtt rtx rxr rxs saa sab sar sas sat sax sba sbb sbr sbs sbt sbx sr- sra srb srr srs srt srx ss- ssa ssb ssr sss sst ssx sta stb str sts stt stx sxs sxt t-x taa tab tar tas tat tax tba tbb tbr tbs tbt tra trb trr trs trt trx tsa tsb tsr tss tst tsx tta ttb ttr tts ttt ttx txs txt xaa xar xas xat xbr xbx xrt xrx xsa xsb xss xst xtr xts xtx xxx