a-a a-b a-i aaa aab aai aar aas aax ab- aba abb abi abr abs abx ai- aia aib aii air ais aix ar- ara arb ari arr ars arx as- asa asb asi asr ass asx ax- axa axi axr axs axx baa bab bai bar bas bax bba bbb bbi bbr bbs bbx bi- bia bib bii bir bis bix bra brb bri brr brs brx bsa bsb bsi bsr bss bsx bxb bxi bxx ia- iaa iab iai iar ias iba ibb ibi ibr ibs ibx iia iib iii iir iis iix ir- ira irb iri irr irs irx is- isa isb isi isr iss ixi ra- raa rab rai rar ras rax rba rbb rbi rbr rbs rbx ria rib rii rir ris rix rra rrb rri rrr rrs rsa rsb rsi rsr rss rsx rxr rxs saa sab sai sar sas sax sba sbb sbi sbr sbs sbx sia sib sii sir sis six sr- sra srb sri srr srs srx ss- ssa ssb ssi ssr sss ssx sxi sxs xaa xar xas xbr xbx xia xii xis xix xrx xsa xsb xsi xss xxi xxx