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actions undo-manager
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Scheme Procedure: **undo-manager-perform** | *undo_manager action*
   Performs the given action and adds it to the undo stack.


Scheme Procedure: **undo-manager-undo** | *undo_manager*
   Undoes the last action.


Scheme Procedure: **undo-manager-redo** | *undo_manager*
   Redoes the last undone action.


