This error arises when a lexical rule can apply to its own output. With spelling-change rules, this isn't a problem in the parsing direction, because the number of times the rule can apply is constrained by the input form. In the generation, direction, however, the form itself is unconstrained, only the semantics. A typical case would be a lexeme-to-lexeme rule that only adds information (e.g. case information). This problem doesn't arise with rules where the DTR (input) and mother (output) are already incompatible (e.g., different values for INFLECTED). One solution is to constrain the type of the daugher on the rule: to lex-item if it's the first affix or to the type of the lexical rule that adds the immediately preceeding affix.

Another possibility (if you're dealing with a highly inflecting language) is that you are exceeding the limit on maximal lexical rule applications (the value of maximal-lex-rule-applications set in lkb/globals.lsp). This value can be changed by editing that file.

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