## Mathematics Subject Classification – MSC2020

Monads (= standard construction, triple or triad), algebras for monads, homology and derived functors for monads [See also 18Gxx] {For functional programming, see also 68N18} 981

Internal categories and groupoids {For double categories, see 18N10; for topological groupoids, see 22A22; for Lie groupoids, see 58H05} 4

Localization of categories, calculus of fractions {For homotopical aspects, see also 18N45, 55P60} 412

Fusion categories, modular tensor categories, modular functors {For applications to topological quantum field theories, see also 57R56; for applications to conformal field theories, see also 81T40} 43