A81

A81 refers to a specific entry in the Universal Decimal Classification system, which organizes library materials by subject. In this system, A81 typically covers works related to the history, philosophy, and foundations of sciences, especially focusing on foundational studies in mathematics, logic, and philosophy. It helps librarians and researchers categorize and locate literature that explores the basic principles and fundamental concepts underlying scientific and mathematical disciplines. Essentially, A81 is a code that groups together scholarly works about the origins, principles, and philosophical aspects of sciences and mathematics.