c-- ccc ccd ccf cco ccr ccx cdc cdd cdf cdo cdr cdx cfc cfd cff cfo cfr cfx co- coc cod cof coo cor cox crc crd crf cro crr crx cxc cxf cxo cxr cxx dcc dcd dcf dco dcr dcx ddc ddd ddf ddo ddr ddx dfc dfd dff dfo dfr dfx doc dod dof doo dor dox drc drd dro drr drx dxc dxd dxo dxr dxx fcc fcd fcf fco fcr fcx fdc fdd fdf fdo fdr fdx ffc ffd fff ffo ffr ffx foc fof foo for fox frc frd frf fro frr fxr fxx oc- occ ocd ocf oco ocr ocx odc odd odf odo odr of- ofc ofd off ofo ofr ofx oo- ooc ood oof ooo oor oox or- orc ord orf oro orr orx ox- oxc oxf oxo oxx rcc rcd rcf rco rcr rcx rdc rdd rdf rdo rdr rdx rfc rfd rff rfo rfr roc rod rof roo ror rox rrc rrd rrf rrr rxr xcd xcf xcr xcx xdc xdf xdr xfx xoc xod xof xoo xor xox xrc xrd xrf xrx xxo xxx