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;
  
  /**
   * An interface representing a syntactic constraint that certain graphs need to
   * obey when adding or removing nodes or edges. See instantiations for more
   * details.
   *
   * @author Joseph Ramsey
   */
  public interface GraphConstraint extends TetradSerializable {
      long serialVersionUID = 23L;
  
      /**
       * Checks to make sure that adding the specified edge will comply with the
       * graph constraint.
       *
       * @param edge  the edge to check.
       * @param graph the graph to check.
       * @return true if adding the edge would satisfy the constraint, false if
       * not.
       */
      boolean isEdgeAddable(Edge edge, Graph graph);
  
      /**
       * Checks to make sure that adding the specified node will comply with the
       * graph constraint.
       *
       * @param node  the node to check.
       * @param graph the graph to check.
       * @return true if adding the node would satisfy the constraint, false if
       * not.
       */
      boolean isNodeAddable(Node node, Graph graph);
  
      /**
       * Checks to make sure that removing the specified edge will comply with the
       * graph constraint.
       *
       * @param edge  the edge to check.
       * @param graph the graph to check.
       * @return true if removing the edge would satisfy the constraint, false if
       * not.
       */
      boolean isEdgeRemovable(Edge edge, Graph graph);
  
      /**
       * Checks to make sure that removing the specified node will comply with the
       * graph constraint.
       *
       * @param node  the node to check.
       * @param graph the graph to check.
       * @return true if removing the node would satisfy the constraint, false, if
       * not.
       */
      boolean isNodeRemovable(Node node, Graph graph);
  
      /**
       * @return this string.
       */
      String toString();
  }
  
  
  
  
  
  