Retain 
  superclass: Tactical-Mission-Task 
  agent: Military-Unit <----> Actor 
  object: Terrain-Feature <----> Location 
  base: Military-Unit <----> Acted on 
  duration: (required) 
 
   
 
  resulting-state: Be-Controlled 
                                agent: MU called "friendly forces" agent of Self 
                                object: Terrain-Feature object of Self 
                                 prevents: Occupy 
                                                     agent: MU called "enemy forces" base of Self 
                                                     destination: Terrain-Feature object of Self 
  
                          Be-Prepared 
                                agent: MU called "friendly forces" agent of Self 
                                object: Attack with 
                                               agent: MU called "enemy forces" base of Self 
                                 
Note: How to encode enemy "use" in (1) below? 
 
------------------- 
 
Retain (A). 
======. 
1. Retain is a tactical mission task in which the commander ensures that a terrain feature controlled by a friendly force remains free of enemy occupation or use. 
2. The commander assigning this task must specify the area to retain and the duration of the retention, which is time- or event-driven. 
3. While a unit is conducting this task, it expects the enemy to attack and prepares to become decisively engaged. 
4. A unit tasked to retain a specific piece of terrain does not necessary have to occupy it. 
