When a file is opened, its contents are loaded into its own individual list. To close a file, simply right-click on the associated list in the List Window (see chapter 9) and select the ``Delete" option. If an object is present in multiple lists, deleting one of those lists will not delete that object from the other lists.
To close all of the loaded files, select the ``Delete All" option in the File menu. In addition to deleting everything currently loaded, this option essentially restores the state of the application to what it was in when the application was started.