code: public Command undoLast() {
          Command lastCommand = undoStack.pop();
          redoStack.push(lastCommand);
          lastCommand.undo();
          return lastCommand;
      }
docs: Pops the last command from the com.github.vatbub.common.core.undo stack, puts it on the redo stack and calls its {@link Command#undo()}-method
  
  @return The command that was undone. <b>Its com.github.vatbub.common.core.undo method was already called!</b>