Add check that POMDP states do not have duplicate actions.

prism/src/explicit/ConstructModel.java

@@ -273,6 +273,15 @@ public class ConstructModel extends PrismComponent
 			// Look at each outgoing choice in turn
 			nc = modelGen.getNumChoices();
 			for (i = 0; i < nc; i++) {
+				// If required, check for duplicate actions here
+				if (modelType.partiallyObservable()) {
+					if (((NondetModel) modelSimple).getChoiceByAction(src, modelGen.getChoiceAction(i)) != -1) {
+						String act = modelGen.getChoiceAction(i) == null ? "" : modelGen.getChoiceAction(i).toString();
+						String err = modelType + " is not allowed duplicate action";
+						err += " (\"" + act + "\") in state " + state.toString(modelGen);
+						throw new PrismException(err);
+					}
+				}
 				// For nondet models, collect transitions in a Distribution
 				if (!justReach && modelType.nondeterministic()) {
 					distr = new Distribution();

prism/src/explicit/NondetModel.java

@@ -75,6 +75,27 @@ public interface NondetModel extends Model
 	 */
 	public Object getAction(int s, int i);
 
+	/**
+	 * Get the index of the (first) choice in state {@code s} with action label {@code action}.
+	 * Action labels (which are {@link Object}s) are tested for equality using {@link Object#equals()}.
+	 * Returns -1 if there is no matching action.
+	 */
+	public default int getChoiceByAction(int s, Object action)
+	{
+		int numChoices = getNumChoices(s);
+		for (int i = 0; i < numChoices; i++) {
+			Object a = getAction(s, i);
+			if (a == null) {
+				if (action == null) {
+					return i;
+				}
+			} else if (a.equals(action)) {
+				return i;
+			}
+		}
+		return -1;
+	}
+
 	/**
 	 * Do all choices in in each state have a unique action label?
 	 * <br><br>