c-- ccc ccd cco ccr cct cdc cdd cdo cdr cdt co- coc cod coo cor cot crc crd cro crr crt ctc ctd cto ctr ctt dcc dcd dco dcr dct ddc ddd ddo ddr ddt doc dod doo dor dot drc drd dro drr drt dtc dtd dto dtr dtt oc- occ ocd oco ocr oct odc odd odo odr odt oo- ooc ood ooo oor oot or- orc ord oro orr ort ot- otc otd oto otr ott rcc rcd rco rcr rct rdc rdd rdo rdr rdt roc rod roo ror rot rrc rrd rrr rrt rtc rtd rto rtr rtt tcc tcd tco tcr tct tdc tdd tdo tdr tdt to- toc tod too tor tot trc trd tro trr trt ttc ttd tto ttr ttt