Segal-type models of higher categories

Abstract

Higher category theory is an exceedingly active area of research, whose rapid growth has been driven by its penetration into a diverse range of scientific fields. Its influence extends through key mathematical disciplines, notably homotopy theory, algebraic geometry and algebra, mathematical physics, to encompass important applications in logic, computer science and beyond. Higher categories provide a unifying language whose greatest strength lies in its ability to bridge between diverse areas and uncover novel applications. In this foundational work we introduce a new approach to higher categories. It builds upon the theory of iterated internal categories, one of the simplest possible higher categorical structures available, by adopting a novel and remarkably simple "weak globularity" postulate and demonstrating that the resulting model provides a fully general theory of weak n-categories. The latter are among the most complex of the higher structures, and are crucial for applications. We show that this new model of "weakly globular n-fold categories" is suitably equivalent to the well studied model of weak n-categories due to Tamsamani and Simpson.