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/*
 *  This file is part of "Tweety", a collection of Java libraries for
 *  logical aspects of artificial intelligence and knowledge representation.
 *
 *  Tweety is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License version 3 as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program. If not, see .
 *
 *  Copyright 2016 The Tweety Project Team 
 */
package net.sf.tweety.commons;

import java.util.*;

import net.sf.tweety.commons.util.*;

/**
 * An entailment relation determines whether a formula is entailed
 * from another formula.
 * 
 * @author Matthias Thimm
 *
 * @param  The type of formula the relation works on.
 */
public abstract class EntailmentRelation {

	/** 
	 * Checks whether the given set of formulas entails the given formula.
	 * @param formulas a collection of formulas.
	 * @param formula some formula.
	 * @return "true" if the set of formulas entails the formula
	 */
	public abstract boolean entails(Collection formulas, T formula);
	
	/**
	 * Checks whether the given set of formulas is consistent.
	 * @param formulas a set of formulas.
	 * @return "true" if the set is consistent.
	 */
	public abstract boolean isConsistent(Collection formulas);
	
	/**
	 * If the collection of formulas is consistent this method
	 * returns some model of it or, if it is inconsistent, null.
	 * @return some model of the formulas or null.
	 */
	public abstract Interpretation getWitness(Collection formulas);
	
	/** 
	 * Checks whether the given set of formulas entails the other set of formulas.
	 * @param formulas a collection of formulas.
	 * @param formulas2 a collection of formulas.
	 * @return "true" if the former entails the latter.
	 */
	public boolean entails(Collection formulas, Collection formulas2){
		for(T formula: formulas)
			if(!this.entails(formulas, formula))
				return false;
		return true;
	}
	
	/** 
	 * Checks whether the first formula entails the second formula.
	 * @param formula a formula.
	 * @param formula2 a formula.
	 * @return "true" if the former entails the latter.
	 */
	public boolean entails(T formula, T formula2){
		Collection formulas = new HashSet();
		formulas.add(formula);
		return this.entails(formulas, formula2);
	}
	
	/** 
	 * Checks whether the first formula entails the other set of formulas.
	 * @param formula a formula.
	 * @param formulas2 a set of formulas.
	 * @return "true" if the former entails the latter.
	 */
	public boolean entails(T formula, Collection  formulas2){
		for(T f: formulas2)
			if(!this.entails(formula, f))
				return false;
		return true;
	}
	
	/**
	 * Checks whether the two formula are equivalent, i.e. whether
	 * the first entails the second and vice versa.
	 * @param formula some formula
	 * @param formula2 some formula
	 * @return "true" iff the two formulas are equivalent.
	 */
	public boolean isEquivalent(T formula, T formula2){
		return this.entails(formula, formula2) && this.entails(formula2, formula);
	}
	
	/**
	 * Retrieves the set of kernels for the given formula
	 * from the given set of formulas.
	 * @param formulas a set of formulas.
	 * @param formula a formula.
	 * @return the collection of kernels
	 */	
	public Collection> getKernels(Collection formulas, T formula){
		Collection> kernels = new HashSet>();
		if(!this.entails(formulas, formula)) return kernels;
		SubsetIterator it = new IncreasingSubsetIterator(new HashSet(formulas));
		boolean superSetOfKernel;
		//double i=0;
		//double pow = Math.pow(2, formulas.size());
		while(it.hasNext()){			
			Set candidate = it.next();
			//System.out.println(++i + " - " + (i/pow * 100) + "% - " + kernels + " - " + candidate.size());
			superSetOfKernel = false;
			for(Collection kernel: kernels){
				if(candidate.containsAll(kernel)){
					superSetOfKernel = true;
					break;
				}
			}			
			if(!superSetOfKernel)
				if(this.entails(candidate, formula))
					kernels.add(candidate);
		}		
		return kernels;		
	}
}