c-- ccc ccf cck cco ccs cct cfc cff cfk cfo cfs cft ckc cko cks ckt co- coc cof cok coo cos cot csc csf csk cso css cst ctc ctf ctk cto cts ctt fcc fcf fck fco fcs fct ffc fff ffk ffo ffs fft fkc fkf fkk fkt foc fof fok foo fos fot fsc fsf fsk fso fss fst ftc ftf ftk fto fts ftt k-t kcc kck kcs kct kfc kff kfo kfs kkc kkk kks kkt koc kof kok koo kos kot ksc ksf ksk kso kss kst ktc ktf ktk kto kts ktt oc- occ ocf ock oco ocs oct of- ofc off ofo ofs oft okc okk oko oks oo- ooc oof ook ooo oos oot os- osc osf osk oso oss ost ot- otc otf otk oto ots ott scc scf sck sco scs sct sfc sff sfk sfo sfs sft sk- skc skf skk sko sks skt soc sof sok soo sos sot ss- ssc ssf ssk sso sss sst stc stf stk sto sts stt tcc tcf tck tco tcs tct tfc tff tfk tfo tfs tft tkc tkk tko tks tkt to- toc tof tok too tos tot tsc tsf tsk tso tss tst ttc ttf ttk tto tts ttt