code: <S extends Storable> void inserted(final MapStorage<S> storage, final S key) {
          addToUndoLog(new Undoable() {
              public void undo() {
                  storage.mapRemove(key);
              }
  
              @Override
              public String toString() {
                  return "undo insert by remove: " + key;
              }
          });
      }
docs: Add to undo log.