Methods and apparatus create codewords of n-state symbols having one of 3 or more states with n-state check symbols. Check symbols are created from independent expressions. Codewords are associated with a matrix for detection of one or more symbols in error and the location of such symbols in error. Symbols in error are reconstructed from symbols not in error, error syndromes and check symbols not in error. Deliberately created errors that can be corrected are used as nuisance errors.