a-a a-b aaa aab aak aas aax aay ab- aba abb abk abs abx aby aka akb akk aks as- asa asb ask ass asx asy ax- axa axk axs axx ay- aya ayk ays ayx baa bab bak bas bax bay bba bbb bbk bbs bbx bby bka bkb bkk bks bkx bsa bsb bsk bss bsx bsy bxb bxx by- bya byk bys ka- kaa kab kak kas kax kay kba kbb kbk kbs kbx kkb kkk kks kky ksa ksb ksk kss kxy kya kys kyx saa sab sak sas sax say sba sbb sbk sbs sbx sby sk- ska skb skk sks skx sky ss- ssa ssb ssk sss ssx sxs sy- sya syb syk sys syx xaa xak xas xbx xkb xks xsa xsb xss xxx xxy xyy yaa yab yak yas yax yay ybs yby yka ykk ysa ysb ysk yss ysy yxa yxy yyb yys yyy