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Category theory is a branch of mathematics that study abstraction of mathematical structures and the relationships between them.  Many concepts in mathematics, computer science and mathematical physics can be phrased in the language of categories and morphisms between categories. Categories were first introduced by Samuel Eilenberg and Saunders Mac Lane in 1942 as a tool in the study of algebraic topology.  Category theory has been jokingly referred to, by some mathematicians, as "abstract nonsense" refers, due to its high level of abstraction.

Category theory is a branch of mathematics that study abstraction of mathematical structures and the relationships between them.  Many concepts in mathematics, computer science and mathematical physics can be phrased in the language of categories and morphisms between categories. Categories were first introduced by Samuel Eilenberg and Saunders Mac Lane in 1942 as a tool in the study of algebraic topology.  Category theory has been jokingly referred to, by some mathematicians, as "abstract nonsense" refers, due to its high level of abstraction.