class Predicate:
    '''an interface for Predicates. No methods are actually implemented'''
    def __init__(self):
        pass
    def holds(self, board, coordinates):
        pass
    def __str__(self):
    	pass
        
class LogicPredicate(Predicate):
    '''an abstract class for logic predicates like AND OR NOT. It implements a constructor that accepts a list of predicates'''
    def __init__(self, *predlist):
        self.predicateList = predlist  
        
class TestPredicate(Predicate):
    '''an abstract class for predicates that actually look at a state It implements an init method that accepts a dictionary that contains the state to check for'''
    def __init__(self, ds):
        self.desiredState = ds  #a dictionary describing the desired state