Schwinger limit

In mathematics, a Preradical is a subfunctor of the identity functor in the category of left modules over a ring with identity. The class of all preradicals over R-mod is denoted by R-pr. Theres is a natural order in R-pr given by, for any two preradicals $\sigma$ and $\tau$ , $\sigma \leq \tau$ , if for any left R-module M, $\sigma M\leq \tau M$ . With this order R-pr becomes a big lattice.