-er a-a a-c aaa aac aae aar aax ac- aca acc ace acr acx aea aec aee aer aex ar- ara arc are arr arx ax- axa axe axr axx c-- caa cac cae car cax cca ccc cce ccr ccx ce- cea cec cee cer cex cra crc cre crr crx cxc cxr cxx eaa eac eae ear eax ec- eca ecc ece ecr ecx eea eec eee eer eex era erc ere err ex- exa exc exe exr exx ra- raa rac rae rar rax rca rcc rce rcr rcx re- rea rec ree rer rex rra rrc rrr rxr xaa xac xar xcr xcx xee xer xex xrc xrx xxx