/*******************************************************************************
    * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
    *
    * All rights reserved. This program and the accompanying materials
    * are made available under the terms of the Eclipse Public License v1.0
    * which accompanies this distribution, and is available at
    * http://www.eclipse.org/legal/epl-v10.html
    *
    * Alternatively, the contents of this file may be used under the terms of
   * either the GNU Lesser General Public License Version 2.1 or later (the
   * "LGPL"), in which case the provisions of the LGPL are applicable instead
   * of those above. If you wish to allow use of your version of this file only
   * under the terms of the LGPL, and not to allow others to use your version of
   * this file under the terms of the EPL, indicate your decision by deleting
   * the provisions above and replace them with the notice and other provisions
   * required by the LGPL. If you do not delete the provisions above, a recipient
   * may use your version of this file under the terms of the EPL or the LGPL.
   * 
   * Based on the pseudo boolean algorithms described in:
   * A fast pseudo-Boolean constraint solver Chai, D.; Kuehlmann, A.
   * Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on
   * Volume 24, Issue 3, March 2005 Page(s): 305 - 317
   * 
   * and 
   * Heidi E. Dixon, 2004. Automating Pseudo-Boolean Inference within a DPLL 
   * Framework. Ph.D. Dissertation, University of Oregon.
   *******************************************************************************/
  package org.sat4j.pb.constraints.pb;
  
  import java.math.BigInteger;
  
  import org.sat4j.core.VecInt;
  import org.sat4j.minisat.constraints.cnf.Lits;
  import org.sat4j.minisat.core.ILits;
  import org.sat4j.minisat.core.VarActivityListener;
  import org.sat4j.specs.IteratorInt;
  
  /**
   * @author parrain TODO To change the template for this generated type comment
   *         go to Window - Preferences - Java - Code Style - Code Templates
   */
  public class ConflictMap extends MapPb implements IConflict {
  
  	private final ILits voc;
  
  	protected boolean hasBeenReduced = false;
  	protected long numberOfReductions = 0;
  
  	/**
  	 * to store the slack of the current resolvant
  	 */
  	protected BigInteger currentSlack;
  
  	protected int currentLevel;
  
  	/**
  	 * allows to access directly to all variables belonging to a particular
  	 * level At index 0, unassigned literals are stored (usually level -1); so
  	 * there is always a step between index and levels.
  	 */
  	protected VecInt[] byLevel;
  
  	/**
  	 * constructs the data structure needed to perform cutting planes
  	 * 
  	 * @param cpb
  	 *            pseudo-boolean constraint which rosed the conflict
  	 * @param level
  	 *            current decision level
  	 * @return a conflict on which cutting plane can be performed.
  	 */
  	public static IConflict createConflict(PBConstr cpb, int level) {
  		return new ConflictMap(cpb, level);
  	}
  
  	ConflictMap(PBConstr cpb, int level) {
  		super(cpb);
  		this.voc = cpb.getVocabulary();
  		this.currentLevel = level;
  		initStructures();
  	}
  
  	private void initStructures() {
  		currentSlack = BigInteger.ZERO;
  		byLevel = new VecInt[levelToIndex(currentLevel) + 1];
  		int ilit, litLevel, index;
  		BigInteger tmp;
  		for (int i = 0; i < size(); i++) {
  			ilit = weightedLits.getLit(i);
  			litLevel = voc.getLevel(ilit);
  			// eventually add to slack
  			tmp = weightedLits.getCoef(i);
  			if ((tmp.signum() > 0)
  					&& (((!voc.isFalsified(ilit)) || litLevel == currentLevel)))
  				currentSlack = currentSlack.add(tmp);
  			// add to byLevel structure
  			index = levelToIndex(litLevel);
  			if (byLevel[index] == null) {
  				byLevel[index] = new VecInt();
 			}
 			byLevel[index].push(ilit);
 		}
 	}
 
 	/**
 	 * convert level into an index in the byLevel structure
 	 * 
 	 * @param level
 	 * @return
 	 */
 	private static final int levelToIndex(int level) {
 		return level + 1;
 	}
 
 	/**
 	 * convert index in the byLevel structure into a level
 	 * 
 	 * @param indLevel
 	 * @return
 	 */
 	private static final int indexToLevel(int indLevel) {
 		return indLevel - 1;
 	}
 
 	/*
 	 * coefficient to be computed.
 	 */
 	protected BigInteger coefMult = BigInteger.ZERO;
 
 	protected BigInteger coefMultCons = BigInteger.ZERO;
 
 	/**
 	 * computes a cutting plane with a pseudo-boolean constraint. this method
 	 * updates the current instance (of ConflictMap).
 	 * 
 	 * @param cpb
 	 *            constraint to compute with the cutting plane
 	 * @param litImplied
 	 *            literal that must be resolved by the cutting plane
 	 * @return an update of the degree of the current instance
 	 */
 	public BigInteger resolve(PBConstr cpb, int litImplied,
 			VarActivityListener val) {
 		assert litImplied > 1;
 		int nLitImplied = litImplied ^ 1;
 		if (cpb == null || !weightedLits.containsKey(nLitImplied)) {
 			// no resolution
 			// undo operation should be anticipated
 			int litLevel = levelToIndex(voc.getLevel(litImplied));
 			int lit = 0;
 			if (byLevel[litLevel] != null) {
 				if (byLevel[litLevel].contains(litImplied)) {
 					lit = litImplied;
 					assert weightedLits.containsKey(litImplied);
 				} else if (byLevel[litLevel].contains(nLitImplied)) {
 					lit = nLitImplied;
 					assert weightedLits.containsKey(nLitImplied);
 				}
 			}
 
 			if (lit > 0) {
 				byLevel[litLevel].remove(lit);
 				if (byLevel[0] == null)
 					byLevel[0] = new VecInt();
 				byLevel[0].push(lit);
 			}
 			return degree;
 		}
 
 		assert slackConflict().signum() <= 0;
 		assert degree.signum() >= 0;
 
 		// coefficients of the constraint must be copied in an other structure
 		// in order to make reduction operations.
 		BigInteger[] coefsCons = null;
 		BigInteger degreeCons = cpb.getDegree();
 
 		// search of the index of the implied literal
 		int ind = 0;
 		while (cpb.get(ind) != litImplied)
 			ind++;
 
 		assert cpb.get(ind) == litImplied;
 		assert cpb.getCoef(ind) != BigInteger.ZERO;
 
 		if (cpb.getCoef(ind).equals(BigInteger.ONE)) {
 			// then we know that the resolvant will still be a conflict (cf.
 			// Dixon's property)
 			coefMultCons = weightedLits.get(nLitImplied);
 			coefMult = BigInteger.ONE;
 			// updating of the degree of the conflict
 			degreeCons = degreeCons.multiply(coefMultCons);
 		} else {
 			if (weightedLits.get(nLitImplied).equals(BigInteger.ONE)) {
 				// then we know that the resolvant will still be a conflict (cf.
 				// Dixon's property)
 				coefMult = cpb.getCoef(ind);
 				coefMultCons = BigInteger.ONE;
 				// updating of the degree of the conflict
 				degree = degree.multiply(coefMult);
 			} else {
 				// pb-constraint has to be reduced
 				// to obtain a conflictual result from the cutting plane
 				WatchPb wpb = (WatchPb) cpb; // DLB Findbugs warning ok
 				coefsCons = wpb.getCoefs();
 				assert positiveCoefs(coefsCons);
 				degreeCons = reduceUntilConflict(litImplied, ind, coefsCons,
 						wpb);
 				// updating of the degree of the conflict
 				degreeCons = degreeCons.multiply(coefMultCons);
 				degree = degree.multiply(coefMult);
 			}
 
 			// coefficients of the conflict must be multiplied by coefMult
 			if (!coefMult.equals(BigInteger.ONE))
 				for (int i = 0; i < size(); i++) {
 					changeCoef(i, weightedLits.getCoef(i).multiply(coefMult));
 				}
 		}
 
 		assert slackConflict().signum() <= 0;
 
 		// cutting plane
 		degree = cuttingPlane(cpb, degreeCons, coefsCons, coefMultCons, val);
 
 		// neither litImplied nor nLitImplied is present in coefs structure
 		assert !weightedLits.containsKey(litImplied);
 		assert !weightedLits.containsKey(nLitImplied);
 		// neither litImplied nor nLitImplied is present in byLevel structure
 		assert getLevelByLevel(litImplied) == -1;
 		assert getLevelByLevel(nLitImplied) == -1;
 		assert degree.signum() > 0;
 		assert slackConflict().signum() <= 0;
 
 		// saturation
 		degree = saturation();
 		assert slackConflict().signum() <= 0;
 
 		return degree;
 	}
 
 	protected BigInteger reduceUntilConflict(int litImplied, int ind,
 			BigInteger[] reducedCoefs, WatchPb wpb) {
 		BigInteger slackResolve = BigInteger.ONE.negate();
 		BigInteger slackThis = BigInteger.ZERO;
 		BigInteger slackIndex;
 		BigInteger slackConflict = slackConflict();
 		BigInteger ppcm;
 		BigInteger reducedDegree = wpb.getDegree();
 		BigInteger previousCoefLitImplied = BigInteger.ZERO;
 		BigInteger tmp;
 		BigInteger coefLitImplied = weightedLits.get(litImplied ^ 1);
 
 		do {
 			if (slackResolve.signum() >= 0) {
 				assert slackThis.signum() > 0;
 				tmp = reduceInConstraint(wpb, reducedCoefs, ind, reducedDegree);
 				assert ((tmp.compareTo(reducedDegree) < 0) && (tmp
 						.compareTo(BigInteger.ONE) >= 0));
 				reducedDegree = tmp;
 			}
 			// search of the multiplying coefficients
 			assert weightedLits.get(litImplied ^ 1).signum() > 0;
 			assert reducedCoefs[ind].signum() > 0;
 
 			if (!reducedCoefs[ind].equals(previousCoefLitImplied)) {
 				assert coefLitImplied.equals(weightedLits.get(litImplied ^ 1));
 				ppcm = ppcm(reducedCoefs[ind], coefLitImplied);
 				assert ppcm.signum() > 0;
 				coefMult = ppcm.divide(coefLitImplied);
 				coefMultCons = ppcm.divide(reducedCoefs[ind]);
 
 				assert coefMultCons.signum() > 0;
 				assert coefMult.signum() > 0;
 				assert coefMult.multiply(coefLitImplied).equals(
 						coefMultCons.multiply(reducedCoefs[ind]));
 				previousCoefLitImplied = reducedCoefs[ind];
 			}
 
 			// slacks computed for each constraint
 			slackThis = wpb.slackConstraint(reducedCoefs, reducedDegree)
 					.multiply(coefMultCons);
 			assert slackConflict.equals(slackConflict());
 			slackIndex = slackConflict.multiply(coefMult);
 			assert slackIndex.signum() <= 0;
 			// estimate of the slack after the cutting plane
 			slackResolve = slackThis.add(slackIndex);
 		} while (slackResolve.signum() >= 0);
 		assert coefMult.multiply(weightedLits.get(litImplied ^ 1)).equals(
 				coefMultCons.multiply(reducedCoefs[ind]));
 		return reducedDegree;
 
 	}
 
 	/**
 	 * computes the slack of the current instance
 	 */
 	public BigInteger slackConflict() {
 		BigInteger poss = BigInteger.ZERO;
 		BigInteger tmp;
 		// for each literal
 		for (int i = 0; i < size(); i++) {
 			tmp = weightedLits.getCoef(i);
 			if (tmp.signum() != 0 && !voc.isFalsified(weightedLits.getLit(i)))
 				poss = poss.add(tmp);
 		}
 		return poss.subtract(degree);
 	}
 
 	public boolean oldIsAssertive(int dl) {
 		BigInteger tmp;
 		int lit;
 		BigInteger slack = computeSlack(dl).subtract(degree);
 		if (slack.signum() < 0)
 			return false;
 		for (int i = 0; i < size(); i++) {
 			tmp = weightedLits.getCoef(i);
 			lit = weightedLits.getLit(i);
 			if ((tmp.signum() > 0)
 					&& (voc.isUnassigned(lit) || voc.getLevel(lit) >= dl)
 					&& (slack.compareTo(tmp) < 0))
 				return true;
 		}
 		return false;
 	}
 
 	// computes a slack with respect to a particular decision level
 	private BigInteger computeSlack(int dl) {
 		BigInteger slack = BigInteger.ZERO;
 		int lit;
 		BigInteger tmp;
 		for (int i = 0; i < size(); i++) {
 			tmp = weightedLits.getCoef(i);
 			lit = weightedLits.getLit(i);
 			if ((tmp.signum() > 0)
 					&& (((!voc.isFalsified(lit)) || voc.getLevel(lit) >= dl)))
 				slack = slack.add(tmp);
 		}
 		return slack;
 	}
 
 	/**
 	 * tests if the conflict is assertive (allows to imply a literal) at a
 	 * particular decision level
 	 * 
 	 * @param dl
 	 *            the decision level
 	 * @return true if the conflict is assertive at the decision level
 	 */
 	public boolean isAssertive(int dl) {
 		assert dl <= currentLevel;
 		assert dl <= currentLevel;
 
 		currentLevel = dl;
 		// assert currentSlack.equals(computeSlack(dl));
 		BigInteger slack = currentSlack.subtract(degree);
 		if (slack.signum() < 0)
 			return false;
 		return isImplyingLiteral(slack);
 	}
 
 	// given the slack already computed, tests if a literal could be implied at
 	// a particular level
 	// uses the byLevel data structure to parse each literal by decision level
 	private boolean isImplyingLiteral(BigInteger slack) {
 		// unassigned literals are tried first
 		int unassigned = levelToIndex(-1);
 		int lit;
 		if (byLevel[unassigned] != null) {
 			for (IteratorInt iterator = byLevel[unassigned].iterator(); iterator
 					.hasNext();) {
 				lit = iterator.next();
 				if (slack.compareTo(weightedLits.get(lit)) < 0) {
 					assertiveLiteral = weightedLits.allLits.get(lit);
 					return true;
 				}
 			}
 		}
 		// then we have to look at every literal at a decision level >=dl
 		BigInteger tmp;
 		int level = levelToIndex(currentLevel);
 		if (byLevel[level] != null)
 			for (IteratorInt iterator = byLevel[level].iterator(); iterator
 					.hasNext();) {
 				lit = iterator.next();
 				tmp = weightedLits.get(lit);
 				if (tmp != null && slack.compareTo(tmp) < 0) {
 					assertiveLiteral = weightedLits.allLits.get(lit);
 					return true;
 				}
 			}
 		return false;
 	}
 
 	// given the slack already computed, tests if a literal could be implied at
 	// a particular level
 	// uses the coefs data structure (where coefficients are decreasing ordered)
 	// to parse each literal
 	private boolean isImplyingLiteralOrdered(int dl, BigInteger slack) {
 		int ilit, litLevel;
 		for (int i = 0; i < size(); i++) {
 			ilit = weightedLits.getLit(i);
 			litLevel = voc.getLevel(ilit);
 			if ((litLevel >= dl || voc.isUnassigned(ilit))
 					&& (slack.compareTo(weightedLits.getCoef(i)) < 0))
 				return true;
 		}
 		return false;
 	}
 
 	/**
 	 * computes the least common factor of two integers (Plus Petit Commun
 	 * Multiple in french)
 	 * 
 	 * @param a
 	 *            first integer
 	 * @param b
 	 *            second integer
 	 * @return the least common factor
 	 */
 	protected static BigInteger ppcm(BigInteger a, BigInteger b) {
 		return a.divide(a.gcd(b)).multiply(b);
 	}
 
 	/**
 	 * constraint reduction : removes a literal of the constraint. The literal
 	 * should be either unassigned or satisfied. The literal can not be the
 	 * literal that should be resolved.
 	 * 
 	 * @param wpb
 	 *            the initial constraint to reduce
 	 * @param coefsBis
 	 *            the coefficients of the constraint wrt which the reduction
 	 *            will be proposed
 	 * @param indLitImplied
 	 *            index in wpb of the literal that should be resolved
 	 * @param degreeBis
 	 *            the degree of the constraint wrt which the reduction will be
 	 *            proposed
 	 * @return new degree of the reduced constraint
 	 */
 	public BigInteger reduceInConstraint(WatchPb wpb,
 			final BigInteger[] coefsBis, final int indLitImplied,
 			final BigInteger degreeBis) {
 		// logger.entering(this.getClass().getName(),"reduceInConstraint");
 		assert degreeBis.compareTo(BigInteger.ONE) > 0;
 		// search of an unassigned literal
 		int lit = -1;
 		for (int ind = 0; (ind < wpb.lits.length) && (lit == -1); ind++)
 			if (coefsBis[ind].signum() != 0 && voc.isUnassigned(wpb.lits[ind])) {
 				assert coefsBis[ind].compareTo(degreeBis) < 0;
 				lit = ind;
 			}
 
 		// else, search of a satisfied literal
 		if (lit == -1)
 			for (int ind = 0; (ind < wpb.lits.length) && (lit == -1); ind++)
 				if ((coefsBis[ind].signum() != 0)
 						&& (voc.isSatisfied(wpb.lits[ind]))
 						&& (ind != indLitImplied))
 					lit = ind;
 
 		// a literal has been found
 		assert lit != -1;
 
 		assert lit != indLitImplied;
 		// logger.finer("Found literal "+Lits.toString(lits[lit]));
 		// reduction can be done
 		BigInteger degUpdate = degreeBis.subtract(coefsBis[lit]);
 		coefsBis[lit] = BigInteger.ZERO;
 
 		// saturation of the constraint
 		degUpdate = saturation(coefsBis, degUpdate);
 
 		assert coefsBis[indLitImplied].signum() > 0;
 		assert degreeBis.compareTo(degUpdate) > 0;
 		return degUpdate;
 	}
 
 	static BigInteger saturation(BigInteger[] coefs, BigInteger degree) {
 		assert degree.signum() > 0;
 		BigInteger minimum = degree;
 		for (int i = 0; i < coefs.length; i++) {
 			if (coefs[i].signum() > 0)
 				minimum = minimum.min(coefs[i]);
 			coefs[i] = degree.min(coefs[i]);
 		}
 		if (minimum.equals(degree) && !degree.equals(BigInteger.ONE)) {
 			// the result is a clause
 			// there is no more possible reduction
 			degree = BigInteger.ONE;
 			for (int i = 0; i < coefs.length; i++)
 				if (coefs[i].signum() > 0)
 					coefs[i] = degree;
 		}
 		return degree;
 	}
 
 	private static boolean positiveCoefs(final BigInteger[] coefsCons) {
 		for (int i = 0; i < coefsCons.length; i++) {
 			if (coefsCons[i].signum() <= 0)
 				return false;
 		}
 		return true;
 	}
 
 	/**
 	 * computes the level for the backtrack : the highest decision level for
 	 * which the conflict is assertive.
 	 * 
 	 * @param maxLevel
 	 *            the lowest level for which the conflict is assertive
 	 * @return the highest level (smaller int) for which the constraint is
 	 *         assertive.
 	 */
 	public int getBacktrackLevel(int maxLevel) {
 		// we are looking for a level higher than maxLevel
 		// where the constraint is still assertive
 		VecInt lits;
 		int level;
 		int indStop = levelToIndex(maxLevel) - 1;
 		int indStart = levelToIndex(0);
 		BigInteger slack = computeSlack(0).subtract(degree);
 		int previous = 0;
 		for (int indLevel = indStart; indLevel <= indStop; indLevel++) {
 			if (byLevel[indLevel] != null) {
 				level = indexToLevel(indLevel);
 				assert computeSlack(level).subtract(degree).equals(slack);
 				if (isImplyingLiteralOrdered(level, slack)) {
 					break;
 				}
 				// updating the new slack
 				lits = byLevel[indLevel];
 				int lit;
 				for (IteratorInt iterator = lits.iterator(); iterator.hasNext();) {
 					lit = iterator.next();
 					if (voc.isFalsified(lit)
 							&& voc.getLevel(lit) == indexToLevel(indLevel))
 						slack = slack.subtract(weightedLits.get(lit));
 				}
 				if (!lits.isEmpty())
 					previous = level;
 			}
 		}
 		assert previous == oldGetBacktrackLevel(maxLevel);
 		return previous;
 	}
 
 	public int oldGetBacktrackLevel(int maxLevel) {
 		int litLevel;
 		int borneMax = maxLevel;
 		assert oldIsAssertive(borneMax);
 		int borneMin = -1;
 		// borneMax is the highest level in the search tree where the constraint
 		// is assertive
 		for (int i = 0; i < size(); i++) {
 			litLevel = voc.getLevel(weightedLits.getLit(i));
 			if (litLevel < borneMax && litLevel > borneMin
 					&& oldIsAssertive(litLevel))
 				borneMax = litLevel;
 		}
 		// the level returned is the first level below borneMax
 		// where there is a literal belonging to the constraint
 		int retour = 0;
 		for (int i = 0; i < size(); i++) {
 			litLevel = voc.getLevel(weightedLits.getLit(i));
 			if (litLevel > retour && litLevel < borneMax) {
 				retour = litLevel;
 			}
 		}
 		return retour;
 	}
 
 	public void updateSlack(int level) {
 		int dl = levelToIndex(level);
 		if (byLevel[dl] != null) {
 			int lit;
 			for (IteratorInt iterator = byLevel[dl].iterator(); iterator
 					.hasNext();) {
 				lit = iterator.next();
 				if (voc.isFalsified(lit))
 					currentSlack = currentSlack.add(weightedLits.get(lit));
 			}
 		}
 	}
 
 	@Override
 	void increaseCoef(int lit, BigInteger incCoef) {
 		if ((!voc.isFalsified(lit)) || voc.getLevel(lit) == currentLevel) {
 			currentSlack = currentSlack.add(incCoef);
 		}
 		assert byLevel[levelToIndex(voc.getLevel(lit))].contains(lit);
 		super.increaseCoef(lit, incCoef);
 	}
 
 	@Override
 	void decreaseCoef(int lit, BigInteger decCoef) {
 		if ((!voc.isFalsified(lit)) || voc.getLevel(lit) == currentLevel) {
 			currentSlack = currentSlack.subtract(decCoef);
 		}
 		assert byLevel[levelToIndex(voc.getLevel(lit))].contains(lit);
 		super.decreaseCoef(lit, decCoef);
 	}
 
 	@Override
 	void setCoef(int lit, BigInteger newValue) {
 		int litLevel = voc.getLevel(lit);
 		if ((!voc.isFalsified(lit)) || litLevel == currentLevel) {
 			if (weightedLits.containsKey(lit))
 				currentSlack = currentSlack.subtract(weightedLits.get(lit));
 			currentSlack = currentSlack.add(newValue);
 		}
 		int indLitLevel = levelToIndex(litLevel);
 		if (!weightedLits.containsKey(lit)) {
 			if (byLevel[indLitLevel] == null) {
 				byLevel[indLitLevel] = new VecInt();
 			}
 			byLevel[indLitLevel].push(lit);
 
 		}
 		assert byLevel[indLitLevel] != null;
 		assert byLevel[indLitLevel].contains(lit);
 		super.setCoef(lit, newValue);
 	}
 
 	@Override
 	void changeCoef(int indLit, BigInteger newValue) {
 		int lit = weightedLits.getLit(indLit);
 		int litLevel = voc.getLevel(lit);
 		if ((!voc.isFalsified(lit)) || litLevel == currentLevel) {
 			if (weightedLits.containsKey(lit))
 				currentSlack = currentSlack.subtract(weightedLits.get(lit));
 			currentSlack = currentSlack.add(newValue);
 		}
 		int indLitLevel = levelToIndex(litLevel);
 		assert weightedLits.containsKey(lit);
 		assert byLevel[indLitLevel] != null;
 		assert byLevel[indLitLevel].contains(lit);
 		super.changeCoef(indLit, newValue);
 	}
 
 	@Override
 	void removeCoef(int lit) {
 		int litLevel = voc.getLevel(lit);
 		if ((!voc.isFalsified(lit)) || litLevel == currentLevel) {
 			currentSlack = currentSlack.subtract(weightedLits.get(lit));
 		}
 		int indLitLevel = levelToIndex(litLevel);
 		assert indLitLevel < byLevel.length;
 		assert byLevel[indLitLevel] != null;
 		assert byLevel[indLitLevel].contains(lit);
 		byLevel[indLitLevel].remove(lit);
 		super.removeCoef(lit);
 	}
 
 	private int getLevelByLevel(int lit) {
 		for (int i = 0; i < byLevel.length; i++)
 			if (byLevel[i] != null && byLevel[i].contains(lit))
 				return i;
 		return -1;
 	}
 
 	public boolean slackIsCorrect(int dl) {
 		return currentSlack.equals(computeSlack(dl));
 	}
 
 	@Override
 	public String toString() {
 		int lit;
 		StringBuffer stb = new StringBuffer();
 		for (int i = 0; i < size(); i++) {
 			lit = weightedLits.getLit(i);
 			stb.append(weightedLits.getCoef(i));
 			stb.append(".");
 			stb.append(Lits.toString(lit));
 			stb.append(" ");
 			stb.append("[");
 			stb.append(voc.valueToString(lit));
 			stb.append("@");
 			stb.append(voc.getLevel(lit));
 			stb.append("]");
 		}
 		return stb.toString() + " >= " + degree; //$NON-NLS-1$
 	}
 
 	public boolean hasBeenReduced() {
 		return hasBeenReduced;
 	}
 
 	public long getNumberOfReductions() {
 		return numberOfReductions;
 	}
 }