Module action

File: sage/categories/action.pyx (starting at line 1)

Group, ring, etc. actions on objects. 

The terminology and notation used is suggestive of groups
acting on sets, but this framework can be used for modules, 
algebras, etc. 

A group action $G \times S \rightarrow S$ is a functor from $G$ to Sets. 

AUTHORS: 
    -- Robert Bradshaw: initial version