a-a a-b a-c aaa aab aac aao aar aas aax ab- aba abb abc abo abr abs abx ac- aca acb acc aco acr acs acx aoa aob aoc aoo aor aos aox ar- ara arb arc aro arr ars arx as- asa asb asc aso asr ass asx ax- axa axo axr axs axx baa bab bac bao bar bas bax bba bbb bbc bbo bbr bbs bbx bca bcb bcc bco bcr bcs bcx boa bob boc boo bor bos box bra brb bro brr brs brx bsa bsb bsc bso bsr bss bsx bxb bxo bxx c-- caa cab cac cao car cas cax cba cbb cbc cbo cbr cbs cbx cca ccb ccc cco ccr ccs ccx co- coa cob coc coo cor cos cox cra crb crc cro crr crs crx csa csb csc cso csr css csx cxc cxo cxr cxs cxx oaa oab oac oao oar oas oax ob- oba obb obc obo obr obs obx oc- oca ocb occ oco ocr ocs ocx oo- ooa oob ooc ooo oor oos oox or- ora orb orc oro orr ors orx os- osa osb osc oso osr oss osx ox- oxa oxb oxc oxo oxx ra- raa rab rac rao rar ras rax rba rbb rbc rbo rbr rbs rbx rca rcb rcc rco rcr rcs rcx roa rob roc roo ror ros rox rra rrb rrc rrr rrs rsa rsb rsc rso rsr rss rsx rxr rxs saa sab sac sao sar sas sax sba sbb sbc sbo sbr sbs sbx sca scb scc sco scr scs scx soa sob soc soo sor sos sox sr- sra srb src sro srr srs srx ss- ssa ssb ssc sso ssr sss ssx sxc sxs xaa xac xar xas xbc xbr xbx xcb xcr xcx xoa xoc xoo xor xos xox xrc xrx xsa xsb xsc xss xxo xxx