a-a a-b a-i aaa aab aai aas aax ab- aba abb abi abs abx ai- aia aib aii ais aix as- asa asb asi ass asx ax- axa axi axs axx baa bab bai bas bax bba bbb bbi bbs bbx bi- bia bib bii bis bix bsa bsb bsi bss bsx bxb bxi bxx ia- iaa iab iai ias iba ibb ibi ibs ibx iia iib iii iis iix is- isa isb isi iss ixi saa sab sai sas sax sba sbb sbi sbs sbx sia sib sii sis six ss- ssa ssb ssi sss ssx sxi sxs xaa xas xbx xia xii xis xix xsa xsb xsi xss xxi xxx