Fix OptimizeDPLL defect discovered by Ruediger.

Author: ctjoreilly

aima-core/src/main/java/aima/core/environment/wumpusworld/HybridWumpusAgent.java

@@ -4,7 +4,6 @@
 import aima.core.agent.EnvironmentViewNotifier;
 import aima.core.agent.Percept;
 import aima.core.agent.impl.AbstractAgent;
-import aima.core.logic.propositional.inference.DPLLSatisfiable;
 import aima.core.logic.propositional.inference.OptimizedDPLL;
 import aima.core.search.framework.SearchForActions;
 import aima.core.search.framework.problem.GeneralProblem;
@@ -94,8 +93,7 @@ public HybridWumpusAgent(int caveDimensions, AgentPosition start) {
 	}
 
 	public HybridWumpusAgent(int caveDimensions, AgentPosition start, EnvironmentViewNotifier notifier) {
-		// kb = new WumpusKnowledgeBase(new OptimizedDPLL(), caveDimensions, start); // buggy?
-		kb = new WumpusKnowledgeBase(new DPLLSatisfiable(), caveDimensions, start);
+		kb = new WumpusKnowledgeBase(new OptimizedDPLL(), caveDimensions, start);
 		this.start = start;
 		this.currentPosition = start;
 		this.notifier = notifier;
@@ -234,7 +232,7 @@ public List<WumpusAction> planRoute(Set<AgentPosition> goals, Set<Room> allowed)
 				new AStarSearch<>(new GraphSearch<>(), new ManhattanHeuristicFunction(goals));
 		Optional<List<WumpusAction>> actions = search.findActions(problem);
 
-		return actions.isPresent() ? actions.get() : Collections.EMPTY_LIST;
+		return actions.isPresent() ? actions.get() : Collections.emptyList();
 	}
 
 	/**

aima-core/src/main/java/aima/core/environment/wumpusworld/WumpusKnowledgeBase.java

@@ -146,37 +146,6 @@ public void disableNavSentences() {
     }
 
     public AgentPosition askCurrentPosition(int t) {
-
-        // There seems to be a bug in OptimizedDPLL (incorrect position computation):
-        // Call with: WumpusAgentDemo, 2x2 cave, OptimizedDPLL (HybridWumpusAgend-Constructor)
-        /*
-        if (t == 4) { // todo
-			System.out.println("Ask L_3_1_1: " + ask(newSymbol(LOCATION, 3, 1, 1))); // false
-			System.out.println("Ask L_3_1_2: " + ask(newSymbol(LOCATION, 3, 1, 2))); // true
-			System.out.println("Ask L_3_2_1: " + ask(newSymbol(LOCATION, 3, 2, 1))); // false
-			System.out.println("Ask L_3_2_2: " + ask(newSymbol(LOCATION, 3, 2, 2))); // false
-			System.out.println("Ask North_3: " + ask(newSymbol(FACING_NORTH, 3))); // false
-			System.out.println("Ask South_3: " + ask(newSymbol(FACING_SOUTH, 3))); // false
-			System.out.println("Ask East_3: " + ask(newSymbol(FACING_EAST, 3))); // true
-			System.out.println("Ask West_3: " + ask(newSymbol(FACING_WEST, 3))); // false
-
-			System.out.println("Ask L_4_1_1: " + ask(newSymbol(LOCATION, 4, 1, 1)) + " !"); // true (incorrect)
-			System.out.println("Ask L_4_2_2: " + ask(newSymbol(LOCATION, 4, 2, 2)) + " !"); // true (correct)
-			System.out.println("Ask North_4: " + ask(newSymbol(FACING_NORTH, 4))); // false
-			System.out.println("Ask South_4: " + ask(newSymbol(FACING_SOUTH, 4))); // false
-			System.out.println("Ask East_4: " + ask(newSymbol(FACING_EAST, 4))); // true
-			System.out.println("Ask West_4: " + ask(newSymbol(FACING_WEST, 4))); // false
-
-			System.out.println("Ask L_5_1_1: " + ask(newSymbol(LOCATION, 5, 1, 1))); // false
-			System.out.println("Ask L_5_1_2: " + ask(newSymbol(LOCATION, 5, 1, 2))); // false
-			System.out.println("Ask L_5_2_1: " + ask(newSymbol(LOCATION, 5, 2, 1))); // false
-			System.out.println("Ask L_5_2_2: " + ask(newSymbol(LOCATION, 5, 2, 2))); // false
-
-			// L_4_1_1 is only constrained by:
-			// L_4_1_1 <=> L_3_1_1 & (~FORWARD_3 | Bump_4) | L_3_1_2 & FACING_SOUTH_3 & FORWARD_3 | L_3_2_1 & FACING_WEST_3 & FORWARD_3
-		}
-		*/
-
         int locX = -1, locY = -1;
         for (int x = 1; x <= getCaveXDimension() && locX == -1; x++) {
             for (int y = 1; y <= getCaveYDimension() && locY == -1; y++) {

aima-core/src/main/java/aima/core/logic/propositional/inference/OptimizedDPLL.java

@@ -85,17 +85,17 @@ public boolean dpll(Set<Clause> clauses, List<PropositionSymbol> symbols,
 		// if P is non-null then
 		if (pAndValue != null) {
 			// return DPLL(clauses, symbols - P, model U {P = value})
-			return dpll(clauses, minus(symbols, pAndValue.getFirst()),
-					model.unionInPlace(pAndValue.getFirst(), pAndValue.getSecond()));
+			return callDPLL(clauses, minus(symbols, pAndValue.getFirst()), model, 
+					pAndValue.getFirst(), pAndValue.getSecond()); 
 		}
 
 		// P, value <- FIND-UNIT-CLAUSE(clauses, model)
 		pAndValue = findUnitClause(clauses, model);
 		// if P is non-null then
 		if (pAndValue != null) {
 			// return DPLL(clauses, symbols - P, model U {P = value})
-			return dpll(clauses, minus(symbols, pAndValue.getFirst()),
-					model.unionInPlace(pAndValue.getFirst(), pAndValue.getSecond()));
+			return callDPLL(clauses, minus(symbols, pAndValue.getFirst()), model, 
+					pAndValue.getFirst(), pAndValue.getSecond());
 		}
 
 		// P <- FIRST(symbols); rest <- REST(symbols)