Any user can remove vandalism from a page, but rollbacks, assistants, and administrators have a "rollback" button to make this easier. To revert the edits of one user to the last version by the previous author:

Click "rollback" on the page history, the user contribution list, or on the diff page. Your revert will be marked as a "minor edit" and given the automatic edit summary "Reverted edits by X to last version by Y."

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