a-a a-b a-c a-z aaa aab aac aas aax aaz ab- aba abb abc abs abx abz ac- aca acb acc acs acx acz as- asa asb asc ass asx asz ax- axa axs axx az- aza azb azs azx azz baa bab bac bas bax baz bba bbb bbc bbs bbx bca bcb bcc bcs bcx bcz bsa bsb bsc bss bsx bxb bxx bza bzs bzz c-- caa cab cac cas cax caz cba cbb cbc cbs cbx cbz cca ccb ccc ccs ccx ccz csa csb csc css csx csz cxc cxs cxx cz- czc saa sab sac sas sax saz sba sbb sbc sbs sbx sca scb scc scs scx ss- ssa ssb ssc sss ssx ssz sxc sxs sza xaa xac xas xbc xbx xcb xcx xsa xsb xsc xss xxx zaa zab zac zas zax zaz zbb zbc zbs zcs zsa zsz zxx zzs zzx zzz