Comodule over a Hopf algebroid

A comodule over a Hopf algebroid is a mathematical structure that generalizes the notion of a comodule over a Hopf algebra. Hopf algebras are algebraic structures that combine aspects of both algebra and coalgebra with additional properties (like the existence of an antipode). A Hopf algebroid is a more general structure that facilitates the study of categories and schemes over a base algebra.