code: ///////////////////////////////////////////////////////////////////////////////
  // For information as to what this class does, see the Javadoc, below.       //
  // Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,       //
  // 2007, 2008, 2009, 2010, 2014, 2015 by Peter Spirtes, Richard Scheines, Joseph   //
  // Ramsey, and Clark Glymour.                                                //
  //                                                                           //
  // This program is free software; you can redistribute it and/or modify      //
  // it under the terms of the GNU General Public License as published by      //
  // the Free Software Foundation; either version 2 of the License, or         //
  // (at your option) any later version.                                       //
  //                                                                           //
  // 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 General Public License for more details.                              //
  //                                                                           //
  // You should have received a copy of the GNU General Public License         //
  // along with this program; if not, write to the Free Software               //
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA //
  ///////////////////////////////////////////////////////////////////////////////
  
  package edu.cmu.tetrad.graph;
  
  import edu.cmu.tetrad.util.TetradSerializable;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.util.*;
  
  /**
   * Stores a triple (x, y, z) of nodes. Note that (x, y, z) = (z, y, x). Useful
   * for marking graphs.
   *
   * @author Joseph Ramsey
   */
  public final class IndependenceFact implements Comparable, TetradSerializable {
      static final long serialVersionUID = 23L;
  
      private Node x;
      private Node y;
      private Set<Node> _z;
  
      /**
       * Constructs a triple of nodes.
       */
      public IndependenceFact(Node x, Node y, List<Node> z) {
          if (x == null || y == null || z == null) {
              throw new NullPointerException();
          }
  
          this.x = x;
          this.y = y;
          this._z = new HashSet<>(z);
      }
  
      public IndependenceFact(Node x, Node y, Node... z) {
          if (x == null || y == null || z == null) {
              throw new NullPointerException();
          }
  
          this.x = x;
          this.y = y;
  
          Set<Node> cond = new HashSet<>();
  
          Collections.addAll(cond, z);
  
  
          this._z = cond;
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       */
      public static IndependenceFact serializableInstance() {
          return new IndependenceFact(new GraphNode("X"), new GraphNode("Y"));
      }
  
      public final Node getX() {
          return x;
      }
  
      public final Node getY() {
          return y;
      }
  
      public final List<Node> getZ() {
          return new LinkedList<>(_z);
      }
  
      public final int hashCode() {
          return 1;
      }
  
      public final boolean equals(Object obj) {
          if (!(obj instanceof IndependenceFact)) {
              return false;
          }
  
          IndependenceFact fact = (IndependenceFact) obj;
  
          Set<String> zString1 = new HashSet<>();
  
          for (Node n : _z) {
              zString1.add(n.getName());
          }
  
          Set<String> zString2 = new HashSet<>();
  
          for (Node n : fact._z) {
              zString2.add(n.getName());
          }
  
          String xN1 = x.getName();
          String xN2 = fact.x.getName();
  
          String yN1 = y.getName();
          String yN2 = fact.y.getName();
  
          return zString1.equals(zString2) && ((xN1.equals(xN2) && yN1.equals(yN2)) || xN1.equals(yN2) && yN1.equals(xN2));
  
  //        return _z.equals(fact._z) && ((x.equals(fact.x) && (y.equals(fact.y))) || (x.equals(fact.y) && (y.equals(fact.x))));
      }
  
      public String toString() {
          StringBuilder builder = new StringBuilder();
  
          builder.append(x).append(" _||_ ").append(y);
  
          if (!_z.isEmpty()) {
              builder.append(" | ");
  
              List<Node> z = new ArrayList<>(this._z);
              Collections.sort(z);
  
              for (int i = 0; i < z.size(); i++) {
                  builder.append(z.get(i));
  
                  if (i < z.size() - 1) {
                      builder.append(", ");
                  }
              }
          }
  
          return builder.toString();
      }
  
      /**
       * Note that this compareTo method gives a lexical ordering for independence facts and doesn't
       * reflect independence fact equality. So sorted sets should not be used to check for
       * independence fact existence, for instance. -jdramsey.
       */
      public int compareTo(Object o) {
          IndependenceFact fact = (IndependenceFact) o;
  
          int c = getX().getName().compareTo(fact.getX().getName());
  
          if (c != 0) return c;
  
          c = getY().getName().compareTo(fact.getY().getName());
  
          if (c != 0) return c;
  
          List<Node> z = getZ();
          List<Node> factZ = fact.getZ();
  
          int max = Math.max(z.size(), factZ.size());
  
          for (int i = 0; i < max; i++) {
              if (z.size() <= i && factZ.size() > i) {
                  return -1;
              }
              if (factZ.size() <= i && z.size() > i) {
                  return +1;
              } else {
                  String s = z.get(i).getName();
                  String s2 = factZ.get(i).getName();
                  c = s.compareTo(s2);
  
                  if (c != 0) return c;
              }
          }
  
          return 0;
      }
  
      /**
       * Adds semantic checks to the default deserialization method. This method
       * must have the standard signature for a readObject method, and the body of
       * the method must begin with "s.defaultReadObject();". Other than that, any
       * semantic checks can be specified and do not need to stay the same from
       * version to version. A readObject method of this form may be added to any
       * class, even if Tetrad sessions were previously saved out using a version
       * of the class that didn't include it. (That's what the
       * "s.defaultReadObject();" is for. See J. Bloch, Effective Java, for help.
       *
       * @throws java.io.IOException
       * @throws ClassNotFoundException
       */
      private void readObject(ObjectInputStream s)
              throws IOException, ClassNotFoundException {
          s.defaultReadObject();
      }
  }
  
  
  
  