1) Module theory 
In mathematics, a comodule or corepresentation is a concept dual to a module. The definition of a comodule over a coalgebra is formed by dualizing the definition of a module over an associative algebra. ==Formal definition== ==Examples== ==Rational comodule== If M is a (right) comodule over the coalgebra C, then M is a (left) module over the dual ...