Left-exact Mittag-Leffler functors of modules.

Let $R$ be an associative ring with unit. This paper deals with various aspects of the category of functors of $\mathcal R$-modules; that is, the category of additive and covariant functors from the category of R-modules to the category of abelian groups. We give several characterizations of left-exact Mittag-Leffler functors of $\mathcal R$-modules.