a-a a-b aaa aab aao aar aas aax ab- aba abb abo abr abs abx aoa aob aoo aor aos aox ar- ara arb aro arr ars arx as- asa asb aso asr ass asx ax- axa axo axr axs axx baa bab bao bar bas bax bba bbb bbo bbr bbs bbx boa bob boo bor bos box bra brb bro brr brs brx bsa bsb bso bsr bss bsx bxb bxo bxx oaa oab oao oar oas oax ob- oba obb obo obr obs obx oo- ooa oob ooo oor oos oox or- ora orb oro orr ors orx os- osa osb oso osr oss osx ox- oxa oxb oxo oxx ra- raa rab rao rar ras rax rba rbb rbo rbr rbs rbx roa rob roo ror ros rox rra rrb rrr rrs rsa rsb rso rsr rss rsx rxr rxs saa sab sao sar sas sax sba sbb sbo sbr sbs sbx soa sob soo sor sos sox sr- sra srb sro srr srs srx ss- ssa ssb sso ssr sss ssx sxs xaa xar xas xbr xbx xoa xoo xor xos xox xrx xsa xsb xss xxo xxx