When books in the library catch fire, liquid carbon dioxide can be used to put out the fire. The reason is that the carbon dioxide fire extinguisher leaves no trace after extinguishing, and will not cause damage to books and files, and can be used to extinguish fires such as books and precision instruments.

So the answer is: the carbon dioxide fire extinguisher does not leave any trace after extinguishing the fire, and will not cause damage to books and files.