a-a aaa aaf aao aas aax af- afa aff afo afs afx aoa aof aoo aos aox as- asa asf aso ass asx ax- axa axo axs axx faa faf fao fas fax ffa fff ffo ffs ffx foa fof foo fos fox fsa fsf fso fss fsx fxs fxx oaa oaf oao oas oax of- ofa off ofo ofs ofx oo- ooa oof ooo oos oox os- osa osf oso oss osx ox- oxa oxf oxo oxx saa saf sao sas sax sfa sff sfo sfs sfx soa sof soo sos sox ss- ssa ssf sso sss ssx sxs xaa xaf xas xfa xfs xfx xoa xof xoo xos xox xsa xss xxo xxx