@inbook {gohnert_flexible_2009, title = {A flexible multi-mode undo mechanism for a collaborative modeling environment}, booktitle = {Groupware: Design, Implementation, and Use}, year = {2009}, note = {00002}, publisher = {Springer}, organization = {Springer}, author = {G{\"o}hnert, Tilman and Nils Malzahn and H. Ulrich Hoppe} }