 Categories for the Working Mathematician

"Categories for the Working Mathematician" is a foundational textbook in category theory written by Saunders Mac Lane, first published in 1971. The book is widely regarded as one of the most influential works in mathematics, particularly in the fields of algebra, topology, and mathematical logic. Category theory itself is a branch of mathematics that focuses on the study of abstract structures and relationships between them. It provides a unifying framework for understanding and formalizing concepts from various areas of mathematics.