4 files changed, 21 insertions, 5 deletions
diff --git a/src/cli/runtime/PersistentArrayIdentityMap.cs b/src/cli/runtime/PersistentArrayIdentityMap.cs
index b6cc57bc..232a143a 100644
--- a/src/cli/runtime/PersistentArrayIdentityMap.cs
+++ b/src/cli/runtime/PersistentArrayIdentityMap.cs
@@ -16,7 +16,14 @@ namespace org.clojure.runtime
  * ArrayMap using identity (==) comparison instead of equals
  */
 public class PersistentArrayIdentityMap : PersistentArrayMap {
-public PersistentArrayIdentityMap() {
+
+new public static PersistentArrayIdentityMap EMPTY = new PersistentArrayIdentityMap();
+
+override public IPersistentMap empty() {
+    return EMPTY;
+}
+
+PersistentArrayIdentityMap() {
 }
 
 public PersistentArrayIdentityMap(Object[] init) :base(init) {
diff --git a/src/cli/runtime/PersistentArrayMap.cs b/src/cli/runtime/PersistentArrayMap.cs
index f6a30be7..ebb217a4 100644
--- a/src/cli/runtime/PersistentArrayMap.cs
+++ b/src/cli/runtime/PersistentArrayMap.cs
@@ -29,7 +29,9 @@ public class PersistentArrayMap : IPersistentMap, ISequential {
 
 internal readonly Object[] array;
 
-public PersistentArrayMap(){
+	public static PersistentArrayMap EMPTY = new PersistentArrayMap();
+
+protected PersistentArrayMap(){
     this.array = RT.EMPTY_ARRAY;
 }
 
@@ -86,7 +88,10 @@ public IPersistentMap remove(Object key) {
     int i = indexOf(key);
     if(i >= 0) //have key, will remove
         {
-        Object[] newArray = new Object[array.Length - 2];
+		int newlen = array.Length - 2;
+		if (newlen == 0)
+			return empty();
+		Object[] newArray = new Object[newlen];
         for(int s=0,d=0;s<array.Length;s += 2)
             {
             if(!equalKey(array[s],key)) //skip removal key
@@ -102,6 +107,10 @@ public IPersistentMap remove(Object key) {
     return this;
 }
 
+virtual public IPersistentMap empty() {
+    return EMPTY;
+}
+
 public Object get(Object key) {
     int i = indexOf(key);
     if(i >= 0)
diff --git a/src/cli/runtime/PersistentHybridIdentityMap.cs b/src/cli/runtime/PersistentHybridIdentityMap.cs
index 069a14fb..e1e420e8 100644
--- a/src/cli/runtime/PersistentHybridIdentityMap.cs
+++ b/src/cli/runtime/PersistentHybridIdentityMap.cs
@@ -34,7 +34,7 @@ override public PersistentArrayMap createArrayMap(Object[] init) {
 }
 
 override internal IPersistentMap createArrayMap() {
-    return new PersistentArrayIdentityMap();
+    return PersistentArrayIdentityMap.EMPTY;
 }
 
 override internal IPersistentMap createHashtableMap(Object[] init) {
diff --git a/src/cli/runtime/PersistentHybridMap.cs b/src/cli/runtime/PersistentHybridMap.cs
index 7c0cc88e..67cbfb28 100644
--- a/src/cli/runtime/PersistentHybridMap.cs
+++ b/src/cli/runtime/PersistentHybridMap.cs
@@ -89,7 +89,7 @@ virtual public PersistentArrayMap createArrayMap(Object[] init) {
 }
 
 virtual internal IPersistentMap createArrayMap() {
-    return new PersistentArrayMap();
+    return PersistentArrayMap.EMPTY;
 }
 
 virtual internal IPersistentMap createHashtableMap(Object[] init) {