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.satlab;
  
  import kodkod.util.ints.IntSet;
  
  
  /**
   * Strategy for reducing the unsatisfiable core of
   * a {@link SATProver}.  
   * @specfield traces: ResolutionTrace[]
   * @specfield nexts: IntSet[]
   * @invariant #traces = #nexts
   * @invariant no disj i,j: [0..#nexts) | traces[i] = traces[j] && nexts[i] = nexts[j]
   * @see SATProver#reduce(ReductionStrategy)  
   * @author Emina Torlak
   */
  public interface ReductionStrategy {
  
  	/**
  	 * Returns the next subtrace of the specified trace to be analyzed, given 
  	 * as a set of indices into the trace.   
  	 * If there are no more subtraces to be analyzed (i.e. the given trace is 
  	 * minimal according to the minimality measure used by this strategy),
  	 * returns the empty set.
  	 * @requires 
  	 * <pre>
  	 * let t = this.traces[#this.traces-1], n = this.nexts[#this.nexts-1] | 
  	 *  unsat(t.elts[n].literals) => 
  	 *   (all i: n.ints | let j = #{k: n.ints | k < i} | t.elts[i].equals(trace.elts[j])) 
  	 *  else
  	 *   trace = t
  	 * </pre>
  	 * @ensures 
  	 * <pre> 
  	 *  let next = { i: int | 0 <= i < trace.size()-1 } |
  	 *   trace.elts[next].antecedents in trace.elts[next] and 
  	 *   (some i: [0..#trace) | i !in next and no trace[i].antecedents) and  
  	 *   this.nexts' = this.nexts + #this.nexts->next and
  	 *   this.traces' = this.traces + #this.traces->trace 
  	 * </pre>
  	 * @return this.nexts'[#this.nexts-1]
  	 */
  	public IntSet next(ResolutionTrace trace);
  	
  }
  