The Library of Congress Classification (LCC) system uses a combination of letters and numbers to represent different subjects and subtopics. The notation consists of a combination of one or more letters, followed by a combination of one or more numbers. The letters generally represent the main class or subclass of the subject, while the numbers represent more specific subtopics within the class or subclass. For example, the notation “QA75.5” might be used to represent the subclass of mathematics dealing with numerical analysis. The LCC notation is used to organize and classify materials in libraries that use the LCC system, and can be used to help patrons find materials on specific subjects.