When incremental treebanking is on (default), the {\tt EBL\_\-TREEBANK} command attempts to reuse stored analyses of corpus examples rather than parsing them again. It considers an analysis of a sentence S safe a) if the only grammar rules that have changed since the stored parse was created are lexical ones involving words not occuring in S, b) the config file and the files it includes have not changed, c) the analysis preferences have not changed.