Most editing rules are syntactic rules rather than information deletions or lexical substitutions. I have already outlined how rules are applied to re- pair ungrammatical structures after constituents have been deleted. Such structure-mending rules are obligatory and often accomplish major re- organizations of surface constituents. They are required particularly but not exclusively after deletion rules. Depronominalization commonly becomes obligatory after deletion of its antecedent; without such deletion, depro- nominalization would be an optional reversal.