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.util.ArrayList;
  import java.util.List;
  
  /**
   * Stores a triple (x, y, z) of nodes. Note that (x, y, z) = (z, y, x). Useful
   * for marking graphs.
   *
   * @author Joseph Ramsey, after Frank Wimberly.
   */
  public final class Triple implements TetradSerializable {
      static final long serialVersionUID = 23L;
  
      // Note: Switching all uses of Underline to Triple, since they did the
      // same thing, and this allows for some useful generalizations, especially
      // since for triples it is always the case that (x, y, z) = (z, y, x).
      private Node x;
      private Node y;
      private Node z;
  
      /**
       * Constructs a triple of nodes.
       */
      public Triple(Node x, Node y, Node z) {
          if (x == null || y == null || z == null) {
              throw new NullPointerException();
          }
  
          this.x = x;
          this.y = y;
          this.z = z;
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       */
      public static Triple serializableInstance() {
          return new Triple(new GraphNode("X"), new GraphNode("Y"), new GraphNode("Z"));
      }
  
      public final Node getX() {
          return x;
      }
  
      public final Node getY() {
          return y;
      }
  
      public final Node getZ() {
          return z;
      }
  
      public final int hashCode() {
          int hash = 17;
          hash += 19 * x.hashCode() * z.hashCode();
          hash += 23 * y.hashCode();
          return hash;
      }
  
      public final boolean equals(Object obj) {
          if (!(obj instanceof Triple)) {
              return false;
          }
  
          Triple triple = (Triple) obj;
          return (x == triple.x && y == triple.y &&
                  z == triple.z)
                  || (x == triple.z && y == triple.y &&
                  z == triple.x);
  //        return (x.equals(triple.x) && y.equals(triple.y) &&
  //                z.equals(triple.z))
  //                || (x.equals(triple.z) && y.equals(triple.y) &&
  //                z.equals(triple.x));
      }
  
      public String toString() {
          return "<" + x + ", " + y + ", " + z + ">";
      }
  
      public boolean alongPathIn(Graph graph) {
          return graph.isAdjacentTo(x, y) && graph.isAdjacentTo(y, z) && x != z;
      }
  
      public static String pathString(Graph graph, Node x, Node y, Node z) {
          List<Node> path = new ArrayList<>();
          path.add(x);
          path.add(y);
          path.add(z);
          return GraphUtils.pathString(path, graph);
      }
  }
  
  
  
  