-er c-- ccc ccd cce ccr ccx cdc cdd cde cdr cdx ce- cec ced cee cer cex crc crd cre crr crx cxc cxr cxx dcc dcd dce dcr dcx ddc ddd dde ddr ddx de- dec ded dee der dex drc drd dre drr drx dxc dxd dxr dxx ec- ecc ecd ece ecr ecx ed- edc edd ede edr edx eec eed eee eer eex erc erd ere err ex- exc exd exe exr exx rcc rcd rce rcr rcx rdc rdd rde rdr rdx re- rec red ree rer rex rrc rrd rrr rxr xcd xcr xcx xdc xde xdr xed xee xer xex xrc xrd xrx xxx