STRIPS filter readme

Code written by Eyal Amir.

First, a brief description of the code. It performs filtering of belief states represented literally in list form. For example '(and made-of-wood (or in-desk out-of-desk) (not (or spherical square))).  Each element of a list starting with "and" or "or" is meant to be in the conjunction or disjunction. The second element of a list beginning with "not" (there should only be one other element) is meant to be the expression that's negated. Fluents can be words (like 'ostritch ) or lists (like '(capital-of russia) ) as long as the words "and", "or", and "not" aren't used in the fluent names. The values of true and false are represented as 'true-value and 'false-value. 

Action/observation pairs are passed to the filter in an external file.  For a STRIPS domain, every action has a single rule, and there are no conditions effects.  The STRIPS filter operates under the assumption that if we are passing a certain action to the filter, then the preconditions for that action are already met.  Thus, when filtering we will also assume that the effects will all occur, since the preconditions are met.  In this version of the STRIPS filter, we assume that the belief state is a conjunction of literals (and observations are literals), so there is no need to find the prime implicates of the belief state after filtering has taken place.

The procedure to call to invoke the filter is main.  The procedure itself takes no parameters, but will pass the following parameters to STRIPS-filter, which will then call STRIPS-filter-ret:
1)-domain file that contains the domain definition (external, .pddl extension)
2)-sequence file(external, .seq extension) that contains action/observation pairs,
3)-initial belief state(external, .bel extension)
4)-file to write end belief state to(external, .bel extension)
5)-variable to indicate if domain is already propositional (T), or if it needs to be propositionalized (nil)
6)-an objects file(external, .obj extension), only used if domain needs to be propositionalized
7)-a flag to indicate if statistics should be collected