a-a a-b a-c aaa aab aac aae aaf aao aas ab- aba abb abc abe abf abo abs ac- aca acb acc ace acf aco acs aea aeb aec aee aef aeo aes af- afa afb afc afe aff afo afs aoa aob aoc aoe aof aoo aos as- asa asb asc ase asf aso ass baa bab bac bae baf bao bas bba bbb bbc bbe bbf bbo bbs bca bcb bcc bce bcf bco bcs be- bea beb bec bee bef beo bes bfa bfb bfc bfe bff bfo bfs boa bob boc boe bof boo bos bsa bsb bsc bse bsf bso bss c-- caa cab cac cae caf cao cas cba cbb cbc cbe cbf cbo cbs cca ccb ccc cce ccf cco ccs ce- cea ceb cec cee cef ceo ces cfa cfb cfc cfe cff cfo cfs co- coa cob coc coe cof coo cos csa csb csc cse csf cso css eaa eab eac eae eaf eao eas eba ebb ebc ebe ebf ebo ebs ec- eca ecb ecc ece ecf eco ecs eea eeb eec eee eef eeo ees ef- efa efb efc efe eff efo efs eo- eoa eob eoc eoe eof eoo eos es- esa esb esc ese esf eso ess faa fab fac fae faf fao fas fba fbb fbc fbe fbf fbo fbs fca fcb fcc fce fcf fco fcs fea feb fec fee fef feo fes ffa ffc ffe fff ffo ffs foa fob foc foe fof foo fos fsa fsb fsc fse fsf fso fss oaa oab oac oae oaf oao oas ob- oba obb obc obe obf obo obs oc- oca ocb occ ocf oco ocs oea oeb oec oee oef oeo oes of- ofa ofb ofc ofe off ofo ofs oo- ooa oob ooc oof ooo oos os- osa osb osc ose osf oso oss saa sab sac sae saf sao sas sba sbb sbc sbe sbf sbo sbs sca scb scc sce scf sco scs se- sea seb sec see sef seo ses sfa sfb sfc sfe sff sfo sfs soa sob soc soe sof soo sos ss- ssa ssb ssc sse ssf sso sss