diff --git a/merkle/iavl.go b/merkle/iavl.go
index 81ee5b01..7ee457bb 100644
--- a/merkle/iavl.go
+++ b/merkle/iavl.go
@@ -4,8 +4,6 @@ import (
     "crypto/sha256"
 )
 
-const HASH_BYTE_SIZE int = 4+32
-
 // Immutable AVL Tree (wraps the Node root)
 
 type IAVLTree struct {
@@ -39,7 +37,7 @@ func (self *IAVLTree) Height() uint8 {
 }
 
 func (self *IAVLTree) Has(key Key) bool {
-    return self.root.Has(self.db, key)
+    return self.root.has(self.db, key)
 }
 
 func (self *IAVLTree) Put(key Key, value Value) (updated bool) {
@@ -59,7 +57,7 @@ func (self *IAVLTree) Save() {
 }
 
 func (self *IAVLTree) Get(key Key) (value Value) {
-    return self.root.Get(self.db, key)
+    return self.root.get(self.db, key)
 }
 
 func (self *IAVLTree) Remove(key Key) (value Value, err error) {
@@ -71,6 +69,36 @@ func (self *IAVLTree) Remove(key Key) (value Value, err error) {
     return value, nil
 }
 
+func (self *IAVLTree) Iterator() NodeIterator {
+    pop := func (stack []*IAVLNode) ([]*IAVLNode, *IAVLNode) {
+        if len(stack) <= 0 {
+            return stack, nil
+        } else {
+            return stack[0:len(stack)-1], stack[len(stack)-1]
+        }
+    }
+
+    stack := make([]*IAVLNode, 0, 10)
+    var cur *IAVLNode = self.root
+    var itr NodeIterator
+    itr = func()(tn Node) {
+        if len(stack) > 0 || cur != nil {
+            for cur != nil {
+                stack = append(stack, cur)
+                cur = cur.leftFilled(self.db)
+            }
+            stack, cur = pop(stack)
+            tn = cur
+            cur = cur.rightFilled(self.db)
+            return tn
+        } else {
+            return nil
+        }
+    }
+    return itr
+}
+
+
 // Node
 
 type IAVLNode struct {
@@ -127,16 +155,6 @@ func (self *IAVLNode) Value() Value {
     return self.value
 }
 
-func (self *IAVLNode) Left(db Db) Node {
-    if self.left == nil { return nil }
-    return self.leftFilled(db)
-}
-
-func (self *IAVLNode) Right(db Db) Node {
-    if self.right == nil { return nil }
-    return self.rightFilled(db)
-}
-
 func (self *IAVLNode) Size() uint64 {
     if self == nil { return 0 }
     return self.size
@@ -147,25 +165,25 @@ func (self *IAVLNode) Height() uint8 {
     return self.height
 }
 
-func (self *IAVLNode) Has(db Db, key Key) (has bool) {
+func (self *IAVLNode) has(db Db, key Key) (has bool) {
     if self == nil { return false }
     if self.key.Equals(key) {
         return true
     } else if key.Less(self.key) {
-        return self.leftFilled(db).Has(db, key)
+        return self.leftFilled(db).has(db, key)
     } else {
-        return self.rightFilled(db).Has(db, key)
+        return self.rightFilled(db).has(db, key)
     }
 }
 
-func (self *IAVLNode) Get(db Db, key Key) (value Value) {
+func (self *IAVLNode) get(db Db, key Key) (value Value) {
     if self == nil { return nil }
     if self.key.Equals(key) {
         return self.value
     } else if key.Less(self.key) {
-        return self.leftFilled(db).Get(db, key)
+        return self.leftFilled(db).get(db, key)
     } else {
-        return self.rightFilled(db).Get(db, key)
+        return self.rightFilled(db).get(db, key)
     }
 }
 
@@ -210,13 +228,6 @@ func (self *IAVLNode) Save(db Db) {
     self.flags |= IAVLNODE_FLAG_PERSISTED
 }
 
-// TODO: don't clear the hash if the value hasn't changed.
-func (self *IAVLNode) Put(db Db, key Key, value Value) (_ Node, updated bool) {
-    node, updated := self.put(db, key, value)
-    if node == nil { panic("unexpected nil node in put") }
-    return node, updated
-}
-
 func (self *IAVLNode) put(db Db, key Key, value Value) (_ *IAVLNode, updated bool) {
     if self == nil {
         return &IAVLNode{key: key, value: value, height: 1, size: 1, hash: nil}, false
@@ -242,14 +253,6 @@ func (self *IAVLNode) put(db Db, key Key, value Value) (_ *IAVLNode, updated boo
     }
 }
 
-func (self *IAVLNode) Remove(db Db, key Key) (newSelf Node, value Value, err error) {
-    newIAVLSelf, value, err := self.remove(db, key)
-    if newIAVLSelf != nil {
-        newSelf = newIAVLSelf
-    }
-    return
-}
-
 func (self *IAVLNode) remove(db Db, key Key) (newSelf *IAVLNode, value Value, err error) {
     if self == nil { return nil, nil, NotFound(key) }
 
@@ -571,10 +574,3 @@ func (self *IAVLNode) lmd(db Db) (*IAVLNode) {
 func (self *IAVLNode) rmd(db Db) (*IAVLNode) {
     return self._md(func(node *IAVLNode)*IAVLNode { return node.rightFilled(db) })
 }
-
-func maxUint8(a, b uint8) uint8 {
-    if a > b {
-        return a
-    }
-    return b
-}
diff --git a/merkle/iavl_test.go b/merkle/iavl_test.go
index 72bdda44..cc11f53e 100644
--- a/merkle/iavl_test.go
+++ b/merkle/iavl_test.go
@@ -35,7 +35,7 @@ func TestImmutableAvlPutHasGetRemove(t *testing.T) {
     }
 
     records := make([]*record, 400)
-    var tree *IAVLNode
+    var node *IAVLNode
     var err error
     var val Value
     var updated bool
@@ -47,50 +47,50 @@ func TestImmutableAvlPutHasGetRemove(t *testing.T) {
     for i := range records {
         r := randomRecord()
         records[i] = r
-        tree, updated = tree.put(nil, r.key, String(""))
+        node, updated = node.put(nil, r.key, String(""))
         if updated {
             t.Error("should have not been updated")
         }
-        tree, updated = tree.put(nil, r.key, r.value)
+        node, updated = node.put(nil, r.key, r.value)
         if !updated {
             t.Error("should have been updated")
         }
-        if tree.Size() != uint64(i+1) {
-            t.Error("size was wrong", tree.Size(), i+1)
+        if node.Size() != uint64(i+1) {
+            t.Error("size was wrong", node.Size(), i+1)
         }
     }
 
     for _, r := range records {
-        if has := tree.Has(nil, r.key); !has {
+        if has := node.has(nil, r.key); !has {
             t.Error("Missing key")
         }
-        if has := tree.Has(nil, randstr(12)); has {
+        if has := node.has(nil, randstr(12)); has {
             t.Error("Table has extra key")
         }
-        if val := tree.Get(nil, r.key); !(val.(String)).Equals(r.value) {
+        if val := node.get(nil, r.key); !(val.(String)).Equals(r.value) {
             t.Error("wrong value")
         }
     }
 
     for i, x := range records {
-        if tree, val, err = tree.remove(nil, x.key); err != nil {
+        if node, val, err = node.remove(nil, x.key); err != nil {
             t.Error(err)
         } else if !(val.(String)).Equals(x.value) {
             t.Error("wrong value")
         }
         for _, r := range records[i+1:] {
-            if has := tree.Has(nil, r.key); !has {
+            if has := node.has(nil, r.key); !has {
                 t.Error("Missing key")
             }
-            if has := tree.Has(nil, randstr(12)); has {
+            if has := node.has(nil, randstr(12)); has {
                 t.Error("Table has extra key")
             }
-            if val := tree.Get(nil, r.key); !(val.(String)).Equals(r.value) {
+            if val := node.get(nil, r.key); !(val.(String)).Equals(r.value) {
                 t.Error("wrong value")
             }
         }
-        if tree.Size() != uint64(len(records) - (i+1)) {
-            t.Error("size was wrong", tree.Size(), (len(records) - (i+1)))
+        if node.Size() != uint64(len(records) - (i+1)) {
+            t.Error("size was wrong", node.Size(), (len(records) - (i+1)))
         }
     }
 }
@@ -138,7 +138,7 @@ func TestTraversals(t *testing.T) {
         }
 
         j := 0
-        itr := Iterator(T.Root());
+        itr := T.Iterator()
         for node := itr(); node != nil; node = itr() {
             if int(node.Key().(Int)) != data[j] {
                 t.Error("key in wrong spot in-order")
@@ -185,7 +185,7 @@ func TestGriffin(t *testing.T) {
             t.Fatalf("Expected %v new hashes, got %v", hashCount, count)
         }
         // nuke hashes and reconstruct hash, ensure it's the same.
-        itr := Iterator(n2)
+        itr := (&IAVLTree{root:n2}).Iterator()
         for node:=itr(); node!=nil; node = itr() {
             if node != nil {
                 node.(*IAVLNode).hash = nil
diff --git a/merkle/ibp.go b/merkle/ibp.go
new file mode 100644
index 00000000..45254230
--- /dev/null
+++ b/merkle/ibp.go
@@ -0,0 +1,579 @@
+package merkle
+
+import (
+    "crypto/sha256"
+)
+
+// Immutable B+ Tree (wraps the Node root)
+
+type IBPTree struct {
+    db      Db
+    root    *IBPNode
+}
+
+func NewIBPTree(db Db) *IBPTree {
+    return &IBPTree{db:db, root:nil}
+}
+
+func NewIBPTreeFromHash(db Db, hash ByteSlice) *IBPTree {
+    root := &IBPNode{
+        hash:   hash,
+        flags:  IBPNODE_FLAG_PERSISTED | IBPNODE_FLAG_PLACEHOLDER,
+    }
+    root.fill(db)
+    return &IBPTree{db:db, root:root}
+}
+
+func (self *IBPTree) Root() Node {
+    return self.root
+}
+
+func (self *IBPTree) Size() uint64 {
+    return self.root.Size()
+}
+
+func (self *IBPTree) Height() uint8 {
+    return self.root.Height()
+}
+
+func (self *IBPTree) Has(key Key) bool {
+    return self.root.has(self.db, key)
+}
+
+func (self *IBPTree) Put(key Key, value Value) (updated bool) {
+    self.root, updated = self.root.put(self.db, key, value)
+    return updated
+}
+
+func (self *IBPTree) Hash() (ByteSlice, uint64) {
+    return self.root.Hash()
+}
+
+func (self *IBPTree) Save() {
+    if self.root.hash == nil {
+        self.root.Hash()
+    }
+    self.root.Save(self.db)
+}
+
+func (self *IBPTree) Get(key Key) (value Value) {
+    return self.root.get(self.db, key)
+}
+
+func (self *IBPTree) Remove(key Key) (value Value, err error) {
+    newRoot, value, err := self.root.remove(self.db, key)
+    if err != nil {
+        return nil, err
+    }
+    self.root = newRoot
+    return value, nil
+}
+
+func (self *IBPTree) Iterator() NodeIterator {
+    /*
+    pop := func(stack []*IBPNode) ([]*IBPNode, *IBPNode) {
+        if len(stack) <= 0 {
+            return stack, nil
+        } else {
+            return stack[0:len(stack)-1], stack[len(stack)-1]
+        }
+    }
+
+    stack := make([]*IBPNode, 0, 10)
+    var cur *IBPNode = self.root
+    var itr NodeIterator
+    itr = func()(tn Node) {
+        if len(stack) > 0 || cur != nil {
+            for cur != nil {
+                stack = append(stack, cur)
+                cur = cur.leftFilled(self.db)
+            }
+            stack, cur = pop(stack)
+            tn = cur
+            cur = cur.rightFilled(self.db)
+            return tn
+        } else {
+            return nil
+        }
+    }
+    return itr
+    */
+    return nil
+}
+
+
+// Node
+
+type IBPNode struct {
+    key     Key
+    value   Value
+    size    uint64
+    height  uint8
+    hash    ByteSlice
+    left    *IBPNode
+    right   *IBPNode
+
+    // volatile
+    flags   byte
+}
+
+const (
+    IBPNODE_FLAG_PERSISTED =   byte(0x01)
+    IBPNODE_FLAG_PLACEHOLDER = byte(0x02)
+
+    IBPNODE_DESC_HAS_VALUE =   byte(0x01)
+    IBPNODE_DESC_HAS_LEFT =    byte(0x02)
+    IBPNODE_DESC_HAS_RIGHT =   byte(0x04)
+)
+
+func (self *IBPNode) Copy() *IBPNode {
+    if self == nil {
+        return nil
+    }
+    return &IBPNode{
+        key:    self.key,
+        value:  self.value,
+        size:   self.size,
+        height: self.height,
+        left:   self.left,
+        right:  self.right,
+        hash:   nil,
+        flags:  byte(0),
+    }
+}
+
+func (self *IBPNode) Equals(other Binary) bool {
+    if o, ok := other.(*IBPNode); ok {
+        return self.hash.Equals(o.hash)
+    } else {
+        return false
+    }
+}
+
+func (self *IBPNode) Key() Key {
+    return self.key
+}
+
+func (self *IBPNode) Value() Value {
+    return self.value
+}
+
+func (self *IBPNode) Size() uint64 {
+    if self == nil { return 0 }
+    return self.size
+}
+
+func (self *IBPNode) Height() uint8 {
+    if self == nil { return 0 }
+    return self.height
+}
+
+func (self *IBPNode) has(db Db, key Key) (has bool) {
+    if self == nil { return false }
+    if self.key.Equals(key) {
+        return true
+    } else if key.Less(self.key) {
+        return self.leftFilled(db).has(db, key)
+    } else {
+        return self.rightFilled(db).has(db, key)
+    }
+}
+
+func (self *IBPNode) get(db Db, key Key) (value Value) {
+    if self == nil { return nil }
+    if self.key.Equals(key) {
+        return self.value
+    } else if key.Less(self.key) {
+        return self.leftFilled(db).get(db, key)
+    } else {
+        return self.rightFilled(db).get(db, key)
+    }
+}
+
+func (self *IBPNode) Hash() (ByteSlice, uint64) {
+    if self == nil { return nil, 0 }
+    if self.hash != nil {
+        return self.hash, 0
+    }
+
+    size := self.ByteSize()
+    buf := make([]byte, size, size)
+    hasher := sha256.New()
+    _, hashCount := self.saveToCountHashes(buf)
+    hasher.Write(buf)
+    self.hash = hasher.Sum(nil)
+
+    return self.hash, hashCount+1
+}
+
+func (self *IBPNode) Save(db Db) {
+    if self == nil {
+        return
+    } else if self.hash == nil {
+        panic("savee.hash can't be nil")
+    }
+    if self.flags & IBPNODE_FLAG_PERSISTED > 0 ||
+       self.flags & IBPNODE_FLAG_PLACEHOLDER > 0 {
+        return
+    }
+
+    // save self
+    buf := make([]byte, self.ByteSize(), self.ByteSize())
+    self.SaveTo(buf)
+    db.Put([]byte(self.hash), buf)
+
+    // save left
+    self.left.Save(db)
+
+    // save right
+    self.right.Save(db)
+
+    self.flags |= IBPNODE_FLAG_PERSISTED
+}
+
+func (self *IBPNode) put(db Db, key Key, value Value) (_ *IBPNode, updated bool) {
+    if self == nil {
+        return &IBPNode{key: key, value: value, height: 1, size: 1, hash: nil}, false
+    }
+
+    self = self.Copy()
+
+    if self.key.Equals(key) {
+        self.value = value
+        return self, true
+    }
+
+    if key.Less(self.key) {
+        self.left, updated = self.leftFilled(db).put(db, key, value)
+    } else {
+        self.right, updated = self.rightFilled(db).put(db, key, value)
+    }
+    if updated {
+        return self, updated
+    } else {
+        self.calcHeightAndSize(db)
+        return self.balance(db), updated
+    }
+}
+
+func (self *IBPNode) remove(db Db, key Key) (newSelf *IBPNode, value Value, err error) {
+    if self == nil { return nil, nil, NotFound(key) }
+
+    if self.key.Equals(key) {
+        if self.left != nil && self.right != nil {
+            if self.leftFilled(db).Size() < self.rightFilled(db).Size() {
+                self, newSelf = self.popNode(db, self.rightFilled(db).lmd(db))
+            } else {
+                self, newSelf = self.popNode(db, self.leftFilled(db).rmd(db))
+            }
+            newSelf.left = self.left
+            newSelf.right = self.right
+            newSelf.calcHeightAndSize(db)
+            return newSelf, self.value, nil
+        } else if self.left == nil {
+            return self.rightFilled(db), self.value, nil
+        } else if self.right == nil {
+            return self.leftFilled(db), self.value, nil
+        } else {
+            return nil, self.value, nil
+        }
+    }
+
+    if key.Less(self.key) {
+        if self.left == nil {
+            return self, nil, NotFound(key)
+        }
+        var newLeft *IBPNode
+        newLeft, value, err = self.leftFilled(db).remove(db, key)
+        if newLeft == self.leftFilled(db) { // not found
+            return self, nil, err
+        } else if err != nil { // some other error
+            return self, value, err
+        }
+        self = self.Copy()
+        self.left = newLeft
+    } else {
+        if self.right == nil {
+            return self, nil, NotFound(key)
+        }
+        var newRight *IBPNode
+        newRight, value, err = self.rightFilled(db).remove(db, key)
+        if newRight == self.rightFilled(db) { // not found
+            return self, nil, err
+        } else if err != nil { // some other error
+            return self, value, err
+        }
+        self = self.Copy()
+        self.right = newRight
+    }
+    self.calcHeightAndSize(db)
+    return self.balance(db), value, err
+}
+
+func (self *IBPNode) ByteSize() int {
+    // 1 byte node descriptor
+    // 1 byte node neight
+    // 8 bytes node size
+    size := 10
+    // key
+    size += 1 // type info
+    size += self.key.ByteSize()
+    // value
+    if self.value != nil {
+        size += 1 // type info
+        size += self.value.ByteSize()
+    } else {
+        size += 1
+    }
+    // children
+    if self.left != nil {
+        size += HASH_BYTE_SIZE
+    }
+    if self.right != nil {
+        size += HASH_BYTE_SIZE
+    }
+    return size
+}
+
+func (self *IBPNode) SaveTo(buf []byte) int {
+    written, _ := self.saveToCountHashes(buf)
+    return written
+}
+
+func (self *IBPNode) saveToCountHashes(buf []byte) (int, uint64) {
+    cur := 0
+    hashCount := uint64(0)
+
+    // node descriptor
+    nodeDesc := byte(0)
+    if self.value != nil { nodeDesc |= IBPNODE_DESC_HAS_VALUE }
+    if self.left != nil  { nodeDesc |= IBPNODE_DESC_HAS_LEFT }
+    if self.right != nil { nodeDesc |= IBPNODE_DESC_HAS_RIGHT }
+    cur += UInt8(nodeDesc).SaveTo(buf[cur:])
+
+    // node height & size
+    cur += UInt8(self.height).SaveTo(buf[cur:])
+    cur += UInt64(self.size).SaveTo(buf[cur:])
+
+    // node key
+    buf[cur] = GetBinaryType(self.key)
+    cur += 1
+    cur += self.key.SaveTo(buf[cur:])
+
+    // node value
+    if self.value != nil {
+        buf[cur] = GetBinaryType(self.value)
+        cur += 1
+        cur += self.value.SaveTo(buf[cur:])
+    }
+
+    // left child
+    if self.left != nil {
+        leftHash, leftCount := self.left.Hash()
+        hashCount += leftCount
+        cur += leftHash.SaveTo(buf[cur:])
+    }
+
+    // right child
+    if self.right != nil {
+        rightHash, rightCount := self.right.Hash()
+        hashCount += rightCount
+        cur += rightHash.SaveTo(buf[cur:])
+    }
+
+    return cur, hashCount
+}
+
+// Given a placeholder node which has only the hash set,
+// load the rest of the data from db.
+// Not threadsafe.
+func (self *IBPNode) fill(db Db) {
+    if self == nil {
+        panic("placeholder can't be nil")
+    } else if self.hash == nil {
+        panic("placeholder.hash can't be nil")
+    }
+    buf := db.Get(self.hash)
+    cur := 0
+    // node header
+    nodeDesc := byte(LoadUInt8(buf))
+    self.height = uint8(LoadUInt8(buf[1:]))
+    self.size = uint64(LoadUInt64(buf[2:]))
+    // key
+    key, cur := LoadBinary(buf, 10)
+    self.key = key.(Key)
+    // value
+    if nodeDesc & IBPNODE_DESC_HAS_VALUE > 0 {
+        self.value, cur = LoadBinary(buf, cur)
+    }
+    // children
+    if nodeDesc & IBPNODE_DESC_HAS_LEFT > 0 {
+        var leftHash ByteSlice
+        leftHash, cur = LoadByteSlice(buf, cur)
+        self.left = &IBPNode{
+            hash:   leftHash,
+            flags:  IBPNODE_FLAG_PERSISTED | IBPNODE_FLAG_PLACEHOLDER,
+        }
+    }
+    if nodeDesc & IBPNODE_DESC_HAS_RIGHT > 0 {
+        var rightHash ByteSlice
+        rightHash, cur = LoadByteSlice(buf, cur)
+        self.right = &IBPNode{
+            hash:   rightHash,
+            flags:  IBPNODE_FLAG_PERSISTED | IBPNODE_FLAG_PLACEHOLDER,
+        }
+    }
+    if cur != len(buf) {
+        panic("buf not all consumed")
+    }
+    self.flags &= ^IBPNODE_FLAG_PLACEHOLDER
+}
+
+func (self *IBPNode) leftFilled(db Db) *IBPNode {
+    if self.left == nil {
+        return nil
+    }
+    if self.left.flags & IBPNODE_FLAG_PLACEHOLDER > 0 {
+        self.left.fill(db)
+    }
+    return self.left
+}
+
+func (self *IBPNode) rightFilled(db Db) *IBPNode {
+    if self.right == nil {
+        return nil
+    }
+    if self.right.flags & IBPNODE_FLAG_PLACEHOLDER > 0 {
+        self.right.fill(db)
+    }
+    return self.right
+}
+
+// Returns a new tree (unless node is the root) & a copy of the popped node.
+// Can only pop nodes that have one or no children.
+func (self *IBPNode) popNode(db Db, node *IBPNode) (newSelf, new_node *IBPNode) {
+    if self == nil {
+        panic("self can't be nil")
+    } else if node == nil {
+        panic("node can't be nil")
+    } else if node.left != nil && node.right != nil {
+        panic("node hnot have both left and right")
+    }
+
+    if self == node {
+
+        var n *IBPNode
+        if node.left != nil {
+            n = node.leftFilled(db)
+        } else if node.right != nil {
+            n = node.rightFilled(db)
+        } else {
+            n = nil
+        }
+        node = node.Copy()
+        node.left = nil
+        node.right = nil
+        node.calcHeightAndSize(db)
+        return n, node
+
+    } else {
+
+        self = self.Copy()
+        if node.key.Less(self.key) {
+            self.left, node = self.leftFilled(db).popNode(db, node)
+        } else {
+            self.right, node = self.rightFilled(db).popNode(db, node)
+        }
+        self.calcHeightAndSize(db)
+        return self, node
+
+    }
+}
+
+func (self *IBPNode) rotateRight(db Db) *IBPNode {
+    self = self.Copy()
+    sl :=  self.leftFilled(db).Copy()
+    slr := sl.right
+
+    sl.right = self
+    self.left = slr
+
+    self.calcHeightAndSize(db)
+    sl.calcHeightAndSize(db)
+
+    return sl
+}
+
+func (self *IBPNode) rotateLeft(db Db) *IBPNode {
+    self = self.Copy()
+    sr :=  self.rightFilled(db).Copy()
+    srl := sr.left
+
+    sr.left = self
+    self.right = srl
+
+    self.calcHeightAndSize(db)
+    sr.calcHeightAndSize(db)
+
+    return sr
+}
+
+func (self *IBPNode) calcHeightAndSize(db Db) {
+    self.height = maxUint8(self.leftFilled(db).Height(), self.rightFilled(db).Height()) + 1
+    self.size = self.leftFilled(db).Size() + self.rightFilled(db).Size() + 1
+}
+
+func (self *IBPNode) calcBalance(db Db) int {
+    if self == nil {
+        return 0
+    }
+    return int(self.leftFilled(db).Height()) - int(self.rightFilled(db).Height())
+}
+
+func (self *IBPNode) balance(db Db) (newSelf *IBPNode) {
+    balance := self.calcBalance(db)
+    if (balance > 1) {
+        if (self.leftFilled(db).calcBalance(db) >= 0) {
+            // Left Left Case
+            return self.rotateRight(db)
+        } else {
+            // Left Right Case
+            self = self.Copy()
+            self.left = self.leftFilled(db).rotateLeft(db)
+            //self.calcHeightAndSize()
+            return self.rotateRight(db)
+        }
+    }
+    if (balance < -1) {
+        if (self.rightFilled(db).calcBalance(db) <= 0) {
+            // Right Right Case
+            return self.rotateLeft(db)
+        } else {
+            // Right Left Case
+            self = self.Copy()
+            self.right = self.rightFilled(db).rotateRight(db)
+            //self.calcHeightAndSize()
+            return self.rotateLeft(db)
+        }
+    }
+    // Nothing changed
+    return self
+}
+
+func (self *IBPNode) _md(side func(*IBPNode)*IBPNode) (*IBPNode) {
+    if self == nil {
+        return nil
+    } else if side(self) != nil {
+        return side(self)._md(side)
+    } else {
+        return self
+    }
+}
+
+func (self *IBPNode) lmd(db Db) (*IBPNode) {
+    return self._md(func(node *IBPNode)*IBPNode { return node.leftFilled(db) })
+}
+
+func (self *IBPNode) rmd(db Db) (*IBPNode) {
+    return self._md(func(node *IBPNode)*IBPNode { return node.rightFilled(db) })
+}
diff --git a/merkle/types.go b/merkle/types.go
index 5015cf7d..ca5a2c18 100644
--- a/merkle/types.go
+++ b/merkle/types.go
@@ -4,6 +4,8 @@ import (
     "fmt"
 )
 
+const HASH_BYTE_SIZE int = 4+32
+
 type Binary interface {
     ByteSize()      int
     SaveTo([]byte)  int
@@ -25,6 +27,21 @@ type Db interface {
     Put([]byte, []byte)
 }
 
+type Node interface {
+    Binary
+
+    Key()           Key
+    Value()         Value
+
+    Size()          uint64
+    Height()        uint8
+
+    Hash()          (ByteSlice, uint64)
+    Save(Db)
+}
+
+type NodeIterator func() Node
+
 type Tree interface {
     Root()          Node
 
@@ -38,30 +55,10 @@ type Tree interface {
 
     Put(Key, Value) bool
     Remove(Key)     (Value, error)
+
+    Iterator()      NodeIterator
 }
 
-type Node interface {
-    Binary
-
-    Key()           Key
-    Value()         Value
-    Left(Db)        Node
-    Right(Db)       Node
-
-    Size()          uint64
-    Height()        uint8
-    Has(Db, Key)    bool
-    Get(Db, Key)    Value
-
-    Hash()          (ByteSlice, uint64)
-    Save(Db)
-
-    Put(Db, Key, Value) (Node, bool)
-    Remove(Db, Key) (Node, Value, error)
-}
-
-type NodeIterator func() Node
-
 func NotFound(key Key) error {
     return fmt.Errorf("Key was not found.")
 }
diff --git a/merkle/util.go b/merkle/util.go
index a5a3c037..cc37f257 100644
--- a/merkle/util.go
+++ b/merkle/util.go
@@ -5,35 +5,6 @@ import (
     "fmt"
 )
 
-func Iterator(node Node) NodeIterator {
-    stack := make([]Node, 0, 10)
-    var cur Node = node
-    var itr NodeIterator
-    itr = func()(tn Node) {
-        if len(stack) > 0 || cur != nil {
-            for cur != nil {
-                stack = append(stack, cur)
-                cur = cur.Left(nil)
-            }
-            stack, cur = pop(stack)
-            tn = cur
-            cur = cur.Right(nil)
-            return tn
-        } else {
-            return nil
-        }
-    }
-    return itr
-}
-
-func pop(stack []Node) ([]Node, Node) {
-    if len(stack) <= 0 {
-        return stack, nil
-    } else {
-        return stack[0:len(stack)-1], stack[len(stack)-1]
-    }
-}
-
 func PrintIAVLNode(node *IAVLNode) {
     fmt.Println("==== NODE")
     printIAVLNode(node, 0)
@@ -68,3 +39,10 @@ func randstr(length int) String {
     panic("unreachable")
 }
 
+func maxUint8(a, b uint8) uint8 {
+    if a > b {
+        return a
+    }
+    return b
+}
+