Choudhary, RajivDewan, Prasun2017-04-152017-04-151995978-94-011-0349-7A general multi-user undo/redo model must satisfy several requirements It must be compatible with an existing single-user undo/redo model, give individual users autonomy in executing undo/redo commands, support undo/redo of remote commands and the remote effects of local commands, be independent of the coupling, multicast, and concurrency control model, and allow undo/redo of arbitrary commands We have developed a multi-user undo/redo model for meeting these requirements The model constructs the command history of a particular user by including all local commands and those remote commands whose results were made visible to that user It allows a user to undo/redo corresponding commands in the command histories of all users of a program Moreover, it allows a user to undo/redo both symmetric user-interface commands and asymmetric collaboration commands We have implemented the model in a collaboration system called Suite In this paper, we motivate, describe, and illustrate these requirements and our modelenText