content: /* 
   * Kodkod -- Copyright (c) 2005-present, Emina Torlak
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  package kodkod.engine.bool;
  
  /** 
   * Represents a boolean value, which may be a {@link kodkod.engine.bool.BooleanFormula formula} 
   * or a {@link kodkod.engine.bool.BooleanConstant constant}.  Boolean formulas are produced by 
   * {@link kodkod.engine.bool.BooleanFactory circuit factories}.  Each value is associated with 
   * an integer label; the labels are unique within a given factory.  
   * A boolean value with a negative label -|l| represents the negation of the value with the positive
   * label |l|. Non-constant values are not shared among factories.  
   * 
   * @specfield op: Operator
   * @specfield label: [-Integer.MAX_VALUE, Integer.MAX_VALUE]
   * @invariant no c: BooleanValue - this | some components.c & components.this && c.label = this.label
   * @author Emina Torlak  
   */
  public abstract class BooleanValue implements Comparable<BooleanValue> {
  
  	BooleanValue() {}
  	
  	/**
  	 * Returns the negation of this boolean value
  	 * @return { f: BooleanFormula | [[f]] = ![[this]] }
  	 */
  	abstract BooleanValue negation();
  	
  	/**
  	 * Returns the label for this value. 
  	 * @return this.label
  	 */
  	public abstract int label();
  	
  	/**
  	 * Returns the operator representing the function
  	 * computed by this gate.
  	 * @return this.op
  	 */
  	public abstract Operator op();
  	
  	/**
  	 * Boolean components are ordered according to their labels.
  	 * Note that the ordering is well defined on components produced by the same factory.
  	 * Specifically, this comparison function is consistent with equals for the components
  	 * produced by the same factory, but may not be for the components produced by different factories. 
  	 * @return 0 if the label of this and other are the same, a negative
  	 * integer if the label of this is smaller than the label of other; and
  	 * a positive integer otherwise.
  	 */
  	public final int compareTo(BooleanValue other) {
  		return label() - other.label();
  	}
  }
  