a-a a-c aaa aac aae aaf aao aax ac- aca acc ace acf aco acx aea aec aee aef aeo aex af- afa afc afe aff afo afx aoa aoc aoe aof aoo aox ax- axa axe axo axx c-- caa cac cae caf cao cax cca ccc cce ccf cco ccx ce- cea cec cee cef ceo cex cfa cfc cfe cff cfo cfx co- coa coc coe cof coo cox cxc cxf cxo cxx eaa eac eae eaf eao eax ec- eca ecc ece ecf eco ecx eea eec eee eef eeo eex ef- efa efc efe eff efo efx eo- eoa eoc eoe eof eoo ex- exa exc exe exo exx faa fac fae faf fao fax fca fcc fce fcf fco fcx fea fec fee fef feo fex ffa ffc ffe fff ffo ffx foa foc foe fof foo fox fxe fxx oaa oac oae oaf oao oax oc- oca occ ocf oco ocx oea oec oee oef oeo oex of- ofa ofc ofe off ofo ofx oo- ooa ooc oof ooo oox ox- oxa oxc oxf oxo oxx xaa xac xaf xcf xcx xee xex xfa xfe xfx xoa xoc xof xoo xox xxo xxx