fff ffm ffo ffr ffx fmf fmm fmo fmr fmx fof fom foo for fox frf frm fro frr fxm fxr fxx m-f m-o m-r mff mfm mfo mfr mmf mmm mmo mmr mmx mof mom moo mor mox mrf mrm mro mrr mrx mxr of- off ofm ofo ofr ofx om- omf omm omo omr omx oo- oof oom ooo oor oox or- orf orm oro orr orx ox- oxf oxo oxx rff rfm rfo rfr rmf rmm rmo rmr rmx rof rom roo ror rox rrf rrm rrr rxr xfm xfx xmf xmm xmo xmr xmx xof xom xoo xor xox xrf xrx xxo xxx