In mathematics, specifically in category theory, an F {\displaystyle F} -coalgebra is a structure defined according to a functor F {\displaystyle F} , with specific properties as defined below. For both algebras and coalgebras, a functor is a convenient and general way of organizing a signature. This has applications in computer science: examples of coalgebras include lazy evaluation, infinite data structures, such as streams, and also transition systems.
F {\displaystyle F} -coalgebras are dual to F {\displaystyle F} -algebras. Just as the class of all algebras for a given signature and equational theory form a variety, so does the class of all F {\displaystyle F} -coalgebras satisfying a given equational theory form a covariety, where the signature is given by F {\displaystyle F} .