diff --git a/SpriteCompiler/AI/AStarSearch.cs b/SpriteCompiler/AI/AStarSearch.cs
index 981bf4e..97ebabd 100644
--- a/SpriteCompiler/AI/AStarSearch.cs
+++ b/SpriteCompiler/AI/AStarSearch.cs
@@ -5,7 +5,7 @@
         where C : IPathCost<C>
     {
         public AStarSearch(AbstractAISearch<A, S, T, C> search)
-            : base(search, new AStarComparator<A, S, T, C>())
+            : base(search) // , new AStarComparator<A, S, T, C>())
         {
         }
 
diff --git a/SpriteCompiler/AI/AbstractAISearch.cs b/SpriteCompiler/AI/AbstractAISearch.cs
index e6e8534..3476114 100644
--- a/SpriteCompiler/AI/AbstractAISearch.cs
+++ b/SpriteCompiler/AI/AbstractAISearch.cs
@@ -6,7 +6,7 @@
 
     public abstract class AbstractAISearch<A, S, T, C>
         where T : ISearchNode<A, S, T, C>
-        where C : IComparable<C>
+        where C : IPathCost<C>
     {
         // Conceptually the expander is responsible for two things:
         //
@@ -68,7 +68,7 @@
             return !solution.Any();
         }
 
-        public IEnumerable<T> Search(ISearchProblem<A, S, C> problem, IQueue<T> fringe, S initialState)
+        public virtual IEnumerable<T> Search(ISearchProblem<A, S, C> problem, IQueue<T> fringe, S initialState)
         {
             fringe.Enqueue(expander.CreateNode(default(T), initialState));
             return ExtendSearch(problem, fringe);
diff --git a/SpriteCompiler/AI/BestFirstSearch.cs b/SpriteCompiler/AI/BestFirstSearch.cs
index a647340..93e9073 100644
--- a/SpriteCompiler/AI/BestFirstSearch.cs
+++ b/SpriteCompiler/AI/BestFirstSearch.cs
@@ -1,5 +1,6 @@
 namespace SpriteCompiler.AI
 {
+    using Adapters;
     using System.Collections.Generic;
 
     public class BestFirstSearch<A, S, T, C> : ISearch<A, S, T, C>
@@ -15,10 +16,10 @@
             this.fringe = fringe;
         }
 
-        public BestFirstSearch(AbstractAISearch<A, S, T, C> search, IComparer<T> comparator)
+        public BestFirstSearch(AbstractAISearch<A, S, T, C> search)
         {
             this.search = search;
-            // this.fringe = new PriorityQueue<T>(INITIAL_CAPACITY, comparator);
+            this.fringe = new QueueAdapter<T, C>();
         }
 
         public IEnumerable<T> Search(ISearchProblem<A, S, C> problem, S initialState)
diff --git a/SpriteCompiler/AI/GraphSearch.cs b/SpriteCompiler/AI/GraphSearch.cs
new file mode 100644
index 0000000..39d9594
--- /dev/null
+++ b/SpriteCompiler/AI/GraphSearch.cs
@@ -0,0 +1,38 @@
+using System;
+using System.Collections.Generic;
+
+namespace SpriteCompiler.AI
+{
+    public class GraphSearch<A, S, T, C> : AbstractAISearch<A, S, T, C>
+        where T : ISearchNode<A, S, T, C>
+        where C : IPathCost<C>
+    {
+        private readonly ISet<S> closed = new HashSet<S>();
+
+        public GraphSearch(INodeExpander<A, S, T, C> expander)
+            : base(expander)
+        {
+        }
+
+        /// <summary>
+        /// Generic graph search.  See page 83 in Russell and Norvig.  This only works in informed
+        /// search if the heuristic is admissible.However, if a heuristic is not admissible and
+        /// you still want to use, that means you should know enough to extend this class or write
+        /// your own Search class.
+        /// </summary>
+        public override IEnumerable<T> Search(ISearchProblem<A, S, C> problem, IQueue<T> fringe, S initialState)
+        {
+            closed.Clear();
+            return base.Search(problem, fringe, initialState);
+        }
+
+        protected override void AddNodes(IQueue<T> fringe, T node, ISearchProblem<A, S, C> problem)
+        {
+            if (!closed.Contains(node.State))
+            {
+                closed.Add(node.State);
+                fringe.AddRange(Expand(problem, node));
+            }
+        }
+    }
+}
diff --git a/SpriteCompiler/AI/IGoalTest.cs b/SpriteCompiler/AI/IGoalTest.cs
new file mode 100644
index 0000000..beed721
--- /dev/null
+++ b/SpriteCompiler/AI/IGoalTest.cs
@@ -0,0 +1,7 @@
+namespace SpriteCompiler.AI
+{
+    public interface IGoalTest<S>
+    {
+        bool IsGoal(S state);
+    }
+}
diff --git a/SpriteCompiler/AI/IHeuristicFunction.cs b/SpriteCompiler/AI/IHeuristicFunction.cs
new file mode 100644
index 0000000..afcf070
--- /dev/null
+++ b/SpriteCompiler/AI/IHeuristicFunction.cs
@@ -0,0 +1,9 @@
+namespace SpriteCompiler.AI
+{
+    using System;
+
+    public interface IHeuristicFunction<S, C> where C : IPathCost<C>
+    {
+        C Eval(S state);
+    }
+}
diff --git a/SpriteCompiler/AI/INodeExpander.cs b/SpriteCompiler/AI/INodeExpander.cs
index 6415d62..6809603 100644
--- a/SpriteCompiler/AI/INodeExpander.cs
+++ b/SpriteCompiler/AI/INodeExpander.cs
@@ -11,7 +11,7 @@
     /// </summary>
     public interface INodeExpander<A, S, T, C>
         where T : ISearchNode<A, S, T, C>
-        where C : IComparable<C>
+        where C : IPathCost<C>
     {
         IEnumerable<T> Expand(ISearchProblem<A, S, C> problem, T node);
         T CreateNode(T parent, S state);
diff --git a/SpriteCompiler/AI/IQueue.cs b/SpriteCompiler/AI/IQueue.cs
index 1f1d4fd..52572ff 100644
--- a/SpriteCompiler/AI/IQueue.cs
+++ b/SpriteCompiler/AI/IQueue.cs
@@ -1,12 +1,15 @@
 namespace SpriteCompiler.AI
 {
     using System;
+    using System.Collections.Generic;
 
     public interface IQueue<T>
     {
         void Clear();
         bool Empty { get; }
         T Remove();
+
         void Enqueue(T item);
+        void AddRange(IEnumerable<T> items);
     }
 }
diff --git a/SpriteCompiler/AI/ISearchNode.cs b/SpriteCompiler/AI/ISearchNode.cs
index e0b18e4..8cb500a 100644
--- a/SpriteCompiler/AI/ISearchNode.cs
+++ b/SpriteCompiler/AI/ISearchNode.cs
@@ -9,13 +9,17 @@
     /// <typeparam name="S">State of the search</typeparam>
     /// <typeparam name="T">Type of the parent</typeparam>
     /// <typeparam name="C">Cost type</typeparam>
-    public interface ISearchNode<A, S, T, C> where C : IComparable<C>
+    public interface ISearchNode<A, S, T, C> : ISearchNode<C> where C : IPathCost<C>
     {
         A Action { get; set; }
         C StepCost { get; set; }
-        C PathCost { get; }
         int Depth { get; }
         S State { get; }
         T Parent { get; }
     }
+
+    public interface ISearchNode<C>
+    {
+        C PathCost { get; }
+    }
 }
diff --git a/SpriteCompiler/AI/IStepCostFunction.cs b/SpriteCompiler/AI/IStepCostFunction.cs
new file mode 100644
index 0000000..5efaccf
--- /dev/null
+++ b/SpriteCompiler/AI/IStepCostFunction.cs
@@ -0,0 +1,9 @@
+namespace SpriteCompiler.AI
+{
+    using System;
+
+    public interface IStepCostFunction<A, S, C> where C : IPathCost<C>
+    {
+        C StepCost(S fromState, A action, S toState);
+    }
+}
diff --git a/SpriteCompiler/AI/ISuccessorFunction.cs b/SpriteCompiler/AI/ISuccessorFunction.cs
new file mode 100644
index 0000000..876c501
--- /dev/null
+++ b/SpriteCompiler/AI/ISuccessorFunction.cs
@@ -0,0 +1,9 @@
+namespace SpriteCompiler.AI
+{
+    using System.Collections.Generic;
+
+    public interface ISuccessorFunction<A, S>
+    {
+        IDictionary<A, S> Successors(S state);
+    }
+}
diff --git a/SpriteCompiler/AI/InformedNodeExpander.cs b/SpriteCompiler/AI/InformedNodeExpander.cs
new file mode 100644
index 0000000..0c8b0ab
--- /dev/null
+++ b/SpriteCompiler/AI/InformedNodeExpander.cs
@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+
+namespace SpriteCompiler.AI
+{
+    public abstract class InformedNodeExpander<A, S, T, C> : INodeExpander<A, S, T, C>
+        where T : HeuristicSearchNode<A, S, T, C>
+        where C : IPathCost<C>
+    {
+        public abstract T CreateNode(T parent, S state);
+
+        public IEnumerable<T> Expand(ISearchProblem<A, S, C> problem, T node)
+        {
+            foreach (var successor in problem.Successors(node.State))
+            {
+                var action = successor.Key;
+                var state = successor.Value;
+                var next = CreateNode(node, state);
+
+                next.Action = action;
+                next.StepCost = problem.StepCost(node.State, action, state);
+                next.Heuristic = problem.Heuristic(state);
+
+                yield return next;
+            }
+        }
+    }
+}
diff --git a/SpriteCompiler/AI/SearchProblem.cs b/SpriteCompiler/AI/SearchProblem.cs
new file mode 100644
index 0000000..d6941fb
--- /dev/null
+++ b/SpriteCompiler/AI/SearchProblem.cs
@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SpriteCompiler.AI
+{
+    public class SearchProblem<A, S, C> : ISearchProblem<A, S, C>
+        where C : IPathCost<C>
+    {
+        private readonly IGoalTest<S> goalTest;
+        private readonly IStepCostFunction<A, S, C> stepCost;
+        private readonly ISuccessorFunction<A, S> successorFn;
+        private readonly IHeuristicFunction<S, C> heuristicFn;
+
+        public SearchProblem(IGoalTest<S> goalTest, IStepCostFunction<A, S, C> stepCost, ISuccessorFunction<A, S> successor, IHeuristicFunction<S, C> heuristicFn)
+        {
+            this.goalTest = goalTest;
+            this.stepCost = stepCost;
+            this.successorFn = successor;
+            this.heuristicFn = heuristicFn;
+        }
+        
+        public IDictionary<A, S> Successors(S state)
+        {
+            return successorFn.Successors(state);
+        }
+
+        public bool IsGoal(S state)
+        {
+            return goalTest.IsGoal(state);
+        }
+
+        public C StepCost(S fromState, A action, S toState)
+        {
+            return stepCost.StepCost(fromState, action, toState);
+        }
+
+        public C Heuristic(S state)
+        {
+            return heuristicFn.Eval(state);
+        }
+    }
+}
diff --git a/SpriteCompiler/AI/TreeSearch.cs b/SpriteCompiler/AI/TreeSearch.cs
new file mode 100644
index 0000000..a28483d
--- /dev/null
+++ b/SpriteCompiler/AI/TreeSearch.cs
@@ -0,0 +1,22 @@
+using System;
+
+namespace SpriteCompiler.AI
+{
+    public class TreeSearch<A, S, T, C> : AbstractAISearch<A, S, T, C>
+        where T : ISearchNode<A, S, T, C>
+        where C : IPathCost<C>
+    {
+        public TreeSearch(INodeExpander<A, S, T, C> expander)
+            : base(expander)
+        {
+        }
+
+        /// <summary>
+        /// Generic tree search. See page 72 in Russell and Norvig
+        /// </summary>
+        protected override void AddNodes(IQueue<T> fringe, T node, ISearchProblem<A, S, C> problem)
+        {
+            fringe.AddRange(Expand(problem, node));
+        }
+    }
+}