diff --git a/src/Aufgabe8Test.java b/src/Aufgabe8Test.java
index 501923f..7dc1331 100644
--- a/src/Aufgabe8Test.java
+++ b/src/Aufgabe8Test.java
@@ -24,16 +24,18 @@ public class Aufgabe8Test {
         map.put(new NamedBody("Hygiea", 8.32E19, new Vector3(), new Vector3()), new Vector3());
         map.put(new NamedBody("Ceres", 9.394E20, new Vector3(), new Vector3()), new Vector3());
 
+        assertEquals(12, map.size());
+
         MassiveIterator iterator = map.getKeys().iterator();
-        int count = 0;
-        while (iterator.hasNext()) {
+        int count;
+        for (count = 0; iterator.hasNext(); count++) {
             if (iterator.next().equals(mars)) {
                 iterator.remove();
             }
-            count++;
         }
         assertEquals(12, count);
         assertEquals(11, map.getKeys().size());
+        assertEquals(11, map.size());
         assertFalse(map.getKeys().contains(mars));
 
         assertThrows(NoSuchElementException.class, iterator::next);
diff --git a/src/BodyForceTreeMap.java b/src/BodyForceTreeMap.java
index a0d894b..5ce1cf4 100644
--- a/src/BodyForceTreeMap.java
+++ b/src/BodyForceTreeMap.java
@@ -87,14 +87,14 @@ public class BodyForceTreeMap {
     }
 
     private String toString(Item item) {
-        String s = "";
+        StringBuilder s = new StringBuilder();
         if (item == null) {
-            return s;
+            return s.toString();
         }
-        s += this.toString(item.right);
-        s += String.format("{%s: %s}\n", item.key, item.value);
-        s += this.toString(item.left);
-        return s;
+        s.append(this.toString(item.right));
+        s.append(String.format("{%s: %s}\n", item.key, item.value));
+        s.append(this.toString(item.left));
+        return s.toString();
     }
 
     /**
diff --git a/src/MassiveForceTreeMap.java b/src/MassiveForceTreeMap.java
index 523fdb1..a15a240 100644
--- a/src/MassiveForceTreeMap.java
+++ b/src/MassiveForceTreeMap.java
@@ -88,14 +88,14 @@ public class MassiveForceTreeMap implements MassiveSet {
     }
 
     private String toString(Item item) {
-        String s = "";
+        StringBuilder s = new StringBuilder();
         if (item == null) {
-            return s;
+            return s.toString();
         }
-        s += this.toString(item.right);
-        s += String.format("{%s: %s}\n", item.key, item.value);
-        s += this.toString(item.left);
-        return s;
+        s.append(this.toString(item.right));
+        s.append(String.format("{%s: %s}\n", item.key, item.value));
+        s.append(this.toString(item.left));
+        return s.toString();
     }
 
     /**
@@ -122,26 +122,36 @@ public class MassiveForceTreeMap implements MassiveSet {
     @Override
     public MassiveIterator iterator() {
         return new MassiveIterator() {
+            private Item last = null;
             private Item next = root.getLeftLeaf();
 
             @Override
             public Massive next() {
                 if (!hasNext()) throw new NoSuchElementException();
 
-                Massive m = next.key;
+                last = next;
                 Item newNext = (next.right != null) ? next.right.getLeftLeaf() : next.parent;
+
                 while (newNext != null && newNext.right == next) {
                     next = newNext;
                     newNext = newNext.parent;
                 }
+
                 next = newNext;
-                return m;
+                return last.key;
             }
 
             @Override
             public boolean hasNext() {
                 return next != null;
             }
+
+            @Override
+            public void remove() {
+                if (last == null) throw new IllegalStateException();
+                removeItem(last);
+                last = null;
+            }
         };
     }
 
@@ -155,18 +165,7 @@ public class MassiveForceTreeMap implements MassiveSet {
         Item item = root;
         while (item != null) {
             if (item.key.equals(element)) {
-                Item newP = null;
-                if (item.left != null) {
-                    newP = item.left.getRightLeaf();
-                } else if (item.right != null) {
-                    newP = item.right.getLeftLeaf();
-                }
-                if (item.parent.left == item) {
-                    item.parent.setLeft(newP);
-                } else {
-                    item.parent.setRight(newP);
-                }
-                size--;
+                removeItem(item);
                 return;
             } else if (item.key.mass() > element.mass()) {
                 item = item.left;
@@ -174,6 +173,44 @@ public class MassiveForceTreeMap implements MassiveSet {
                 item = item.right;
             }
         }
+        throw new NoSuchElementException();
+    }
+
+    private void removeItem(Item item) {
+        size--;
+        Item newP = null;
+
+        if (item.left != null) {
+            newP = item.left.getRightLeaf();
+            if (newP != item.left) {
+                newP.parent.setRight(newP.left);
+                newP.setLeft(item.left);
+            }
+            newP.setRight(item.right);
+        } else if (item.right != null) {
+            newP = item.right.getLeftLeaf();
+            if (newP != item.right) {
+                newP.parent.setLeft(newP.right);
+                newP.setRight(item.right);
+            }
+            newP.setLeft(item.left);
+        }
+
+        if (newP == null) {
+            root = null;
+            return;
+        }
+
+        if (item.parent != null) {
+            if (item.parent.left == item) {
+                item.parent.setLeft(newP);
+            } else {
+                item.parent.setRight(newP);
+            }
+        } else {
+            root = newP;
+            newP.parent = null;
+        }
     }
 
     @Override
@@ -220,17 +257,13 @@ public class MassiveForceTreeMap implements MassiveSet {
 
         public Item getLeftLeaf() {
             Item cur = this;
-            while (cur.left != null) {
-                cur = cur.left;
-            }
+            while (cur.left != null) cur = cur.left;
             return cur;
         }
 
         public Item getRightLeaf() {
             Item cur = this;
-            while (cur.right != null) {
-                cur = cur.right;
-            }
+            while (cur.right != null) cur = cur.right;
             return cur;
         }
     }