However, the classification of libraries is mostly based on the combination of majors and letters. Because most libraries are public welfare, the books in them may be more comprehensive than those in bookstores in some aspects, and they are more suitable for querying truly professional books.

Classification method: the professional category is a big category, and then it is divided into small categories according to letters. For example, there are two books in the literature and history category-Jia Pingwa's "The Wasted Capital" and "The Missing Wolf", which are in the F category and the H category respectively. Just use this when inquiring.