fff ffi ffo ffs ffx fif fii fis fix fof foi foo fos fox fsf fsi fso fss fsx fxi fxs fxx i-f iff ifi ifo ifs ifx iif iii iio iis iix io- iof ioi ioo ios is- isf isi iso iss ixi o-i of- off ofi ofo ofs ofx oif oii oio ois oo- oof ooi ooo oos oox os- osf osi oso oss osx ox- oxf oxi oxo oxx sff sfi sfo sfs sfx sif sii sio sis six sof soi soo sos sox ss- ssf ssi sso sss ssx sxi sxs xfs xfx xii xio xis xix xof xoi xoo xos xox xsi xss xxi xxo xxx