@Override
 protected void perform(org.lgna.croquet.history.CompletionStep<?> step) {
   org.lgna.croquet.undo.UndoHistory historyManager =
       this.documentFrame.getDocument().getUndoHistory(org.lgna.croquet.Application.PROJECT_GROUP);
   this.performInternal(historyManager);
   step.finish();
 }
 @Override
 protected void perform(org.lgna.croquet.history.CompletionStep<?> step) {
   this.numberModel.negate();
   step.finish();
 }
 @Override
 protected void perform(org.lgna.croquet.history.CompletionStep<?> step) {
   this.numberModel.replaceSelection(this.numeral);
   step.finish();
 }