diff --git a/merkle/iavl.go b/merkle/iavl.go
index d360339b7..02043462e 100644
--- a/merkle/iavl.go
+++ b/merkle/iavl.go
@@ -1,6 +1,7 @@
 package merkle
 
 import (
+    //"fmt"
     "hash"
     "crypto/sha256"
 )
@@ -100,18 +101,19 @@ func (self *IAVLNode) Get(key Sortable) (value interface{}, err error) {
     }
 }
 
-// Copies and pops node from the tree.
-// Returns a new tree (unless node is the root) & new (popped) node.
+// 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 *IAVLNode) pop_node(node *IAVLNode) (new_self, new_node *IAVLNode) {
-    if node == nil {
+    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 must not have both left and right")
     }
 
-    if self == nil {
-        return nil, node.Copy(true)
-    } else if self == node {
+    if self == node {
+
         var n *IAVLNode
         if node.left != nil {
             n = node.left
@@ -124,18 +126,19 @@ func (self *IAVLNode) pop_node(node *IAVLNode) (new_self, new_node *IAVLNode) {
         node.left = nil
         node.right = nil
         return n, node
-    }
-
-    self = self.Copy(false)
 
-    if node.key.Less(self.key) {
-        self.left, node = self.left.pop_node(node)
     } else {
-        self.right, node = self.right.pop_node(node)
-    }
 
-    self.height = max(self.left.Height(), self.right.Height()) + 1
-    return self, node
+        self = self.Copy(false)
+        if node.key.Less(self.key) {
+            self.left, node = self.left.pop_node(node)
+        } else {
+            self.right, node = self.right.pop_node(node)
+        }
+        self.calc_height()
+        return self, node
+
+    }
 }
 
 // Pushes the node to the tree, returns a new tree
@@ -156,51 +159,74 @@ func (self *IAVLNode) push_node(node *IAVLNode) *IAVLNode {
     } else {
         self.right = self.right.push_node(node)
     }
-    self.height = max(self.left.Height(), self.right.Height()) + 1
+    self.calc_height()
     return self
 }
 
 func (self *IAVLNode) rotate_right() *IAVLNode {
-    if self == nil {
-        return self
-    }
-    if self.left == nil {
-        return self
-    }
-    return self.rotate(self.left.rmd)
+    self = self.Copy(false)
+    sl :=  self.left.Copy(false)
+    slr := sl.right
+
+    sl.right = self
+    self.left = slr
+
+    self.calc_height()
+    sl.calc_height()
+
+    return sl
 }
 
 func (self *IAVLNode) rotate_left() *IAVLNode {
-    if self == nil {
-        return self
-    }
-    if self.right == nil {
-        return self
-    }
-    return self.rotate(self.right.lmd)
+    self = self.Copy(false)
+    sr :=  self.right.Copy(false)
+    srl := sr.left
+
+    sr.left = self
+    self.right = srl
+
+    self.calc_height()
+    sr.calc_height()
+
+    return sr
 }
 
-func (self *IAVLNode) rotate(get_new_root func() *IAVLNode) *IAVLNode {
-    self, new_root := self.pop_node(get_new_root())
-    new_root.left = self.left
-    new_root.right = self.right
-    self.hash = nil
-    self.left = nil
-    self.right = nil
-    return new_root.push_node(self)
+func (self *IAVLNode) calc_height() {
+    self.height = max(self.left.Height(), self.right.Height()) + 1
 }
 
-func (self *IAVLNode) balance() *IAVLNode {
+func (self *IAVLNode) calc_balance() int {
     if self == nil {
-        return self
+        return 0
     }
-    for abs(self.left.Height() - self.right.Height()) > 2 {
-        if self.left.Height() > self.right.Height() {
-            self = self.rotate_right()
+    return self.left.Height() - self.right.Height()
+}
+
+func (self *IAVLNode) balance() (new_self *IAVLNode) {
+    balance := self.calc_balance()
+    if (balance > 1) {
+        if (self.left.calc_balance() >= 0) {
+            // Left Left Case
+            return self.rotate_right()
         } else {
-            self = self.rotate_left()
+            // Left Right Case
+            self = self.Copy(false)
+            self.left = self.left.rotate_left()
+            return self.rotate_right()
         }
     }
+    if (balance < -1) {
+        if (self.right.calc_balance() <= 0) {
+            // Right Right Case
+            return self.rotate_left()
+        } else {
+            // Right Left Case
+            self = self.Copy(false)
+            self.right = self.right.rotate_right()
+            return self.rotate_left()
+        }
+    }
+    // Nothing changed
     return self
 }
 
@@ -222,31 +248,29 @@ func (self *IAVLNode) Put(key Sortable, value interface{}) (_ *IAVLNode, updated
     } else {
         self.right, updated = self.right.Put(key, value)
     }
-    self.height = max(self.left.Height(), self.right.Height()) + 1
-
-    if !updated {
-        self.height += 1
+    if updated {
+        return self, updated
+    } else {
+        self.calc_height()
         return self.balance(), updated
     }
-    return self, updated
 }
 
-func (self *IAVLNode) Remove(key Sortable) (_ *IAVLNode, value interface{}, err error) {
+func (self *IAVLNode) Remove(key Sortable) (new_self *IAVLNode, value interface{}, err error) {
     if self == nil {
         return nil, nil, NotFound(key)
     }
 
     if self.key.Equals(key) {
         if self.left != nil && self.right != nil {
-            var new_root *IAVLNode
             if self.left.Size() < self.right.Size() {
-                self, new_root = self.pop_node(self.right.lmd())
+                self, new_self = self.pop_node(self.right.lmd())
             } else {
-                self, new_root = self.pop_node(self.left.rmd())
+                self, new_self = self.pop_node(self.left.rmd())
             }
-            new_root.left = self.left
-            new_root.right = self.right
-            return new_root, self.value, nil
+            new_self.left = self.left
+            new_self.right = self.right
+            return new_self, self.value, nil
         } else if self.left == nil {
             return self.right, self.value, nil
         } else if self.right == nil {
@@ -256,20 +280,35 @@ func (self *IAVLNode) Remove(key Sortable) (_ *IAVLNode, value interface{}, err
         }
     }
 
-    self = self.Copy(true)
-
     if key.Less(self.key) {
-        self.left, value, err = self.left.Remove(key)
-    } else {
-        self.right, value, err = self.right.Remove(key)
-    }
-    if err == nil {
-        self.hash = nil
-        self.height = max(self.left.Height(), self.right.Height()) + 1
-        return self.balance(), value, err
+        if self.left == nil {
+            return self, nil, NotFound(key)
+        }
+        var new_left *IAVLNode
+        new_left, value, err = self.left.Remove(key)
+        if new_left == self.left { // not found
+            return self, nil, err
+        } else if err != nil { // some other error
+            return self, value, err
+        }
+        self = self.Copy(false)
+        self.left = new_left
     } else {
-        return self, value, err
+        if self.right == nil {
+            return self, nil, NotFound(key)
+        }
+        var new_right *IAVLNode
+        new_right, value, err = self.right.Remove(key)
+        if new_right == self.right { // not found
+            return self, nil, err
+        } else if err != nil { // some other error
+            return self, value, err
+        }
+        self = self.Copy(false)
+        self.right = new_right
     }
+    self.calc_height()
+    return self.balance(), value, err
 }
 
 func (self *IAVLNode) Height() int {
@@ -296,16 +335,12 @@ func (self *IAVLNode) Value() interface{} {
 }
 
 func (self *IAVLNode) Left() Node {
-    if self.left == nil {
-        return nil
-    }
+    if self.left == nil { return nil }
     return self.left
 }
 
 func (self *IAVLNode) Right() Node {
-    if self.right == nil {
-        return nil
-    }
+    if self.right == nil { return nil }
     return self.right
 }
 
diff --git a/merkle/iavl_test.go b/merkle/iavl_test.go
index 47f149c06..94fce5434 100644
--- a/merkle/iavl_test.go
+++ b/merkle/iavl_test.go
@@ -3,6 +3,7 @@ package merkle
 import "testing"
 
 import (
+    "fmt"
     "os"
     "bytes"
     "math/rand"
@@ -150,14 +151,6 @@ func TestTraversals(t *testing.T) {
     var order []int = []int{
         6, 1, 8, 2, 4 , 9 , 5 , 7 , 0 , 3 ,
     }
-    /*
-    var preorder []int = []int {
-        17, 7, 5, 1, 12, 9, 13, 19, 18, 20,
-    }
-    var postorder []int = []int {
-        1, 5, 9, 13, 12, 7, 18, 20, 19, 17,
-    }
-    */
 
     test := func(T Tree) {
         t.Logf("%T", T)
@@ -177,24 +170,106 @@ func TestTraversals(t *testing.T) {
             }
             j += 1
         }
+    }
+    test(NewIAVLTree())
+}
 
-        /*
-        j = 0
-        for tn, next := tree.TraverseTreePreOrder(T.Root())(); next != nil; tn, next = next () {
-            if int(tn.Key().(Int)) != preorder[j] {
-                t.Error("key in wrong spot pre-order")
-            }
-            j += 1
+func BenchmarkSha256(b *testing.B) {
+    b.StopTimer()
+
+    str := []byte(randstr(32))
+
+    ransha256 := func() []byte {
+        return CalcSha256(str)
+    }
+
+    b.StartTimer()
+    for i := 0; i < b.N; i++ {
+        ransha256()
+    }
+}
+
+// from http://stackoverflow.com/questions/3955680/how-to-check-if-my-avl-tree-implementation-is-correct
+func TestGriffin(t *testing.T) {
+    N := func(l *IAVLNode, i int, r *IAVLNode) *IAVLNode {
+        n := &IAVLNode{Int32(i), nil, -1, nil, l, r}
+        n.calc_height()
+        return n
+    }
+    var P func(*IAVLNode) string
+    P = func(n *IAVLNode) string {
+        if n.left == nil && n.right == nil {
+            return fmt.Sprintf("%v", n.key)
+        } else if n.left == nil {
+            return fmt.Sprintf("(- %v %v)", n.key, P(n.right))
+        } else if n.right == nil {
+            return fmt.Sprintf("(%v %v -)", P(n.left), n.key)
+        } else {
+            return fmt.Sprintf("(%v %v %v)", P(n.left), n.key, P(n.right))
         }
+    }
 
-        j = 0
-        for tn, next := tree.TraverseTreePostOrder(T.Root())(); next != nil; tn, next = next () {
-            if int(tn.Key().(Int)) != postorder[j] {
-                t.Error("key in wrong spot post-order")
-            }
-            j += 1
+    expectPut := func(n *IAVLNode, i int, repr string) {
+        n2, updated := n.Put(Int32(i), nil)
+        if updated == true || P(n2) != repr {
+            t.Fatalf("Adding %v to %v:\nExpected         %v\nUnexpectedly got %v updated:%v",
+                i, P(n), repr, P(n2), updated)
         }
-        */
     }
-    test(NewIAVLTree())
+
+    expectRemove := func(n *IAVLNode, i int, repr string) {
+        n2, value, err := n.Remove(Int32(i))
+        if value != nil || err != nil || P(n2) != repr {
+            t.Fatalf("Removing %v from %v:\nExpected         %v\nUnexpectedly got %v value:%v err:%v",
+                i, P(n), repr, P(n2), value, err)
+        }
+    }
+
+    //////// Test Put cases:
+
+    // Case 1:
+    n1 := N(N(nil, 4, nil), 20, nil)
+    if P(n1) != "(4 20 -)" { t.Fatalf("Got %v", P(n1)) }
+
+    expectPut(n1, 15, "(4 15 20)")
+    expectPut(n1, 8, "(4 8 20)")
+
+    // Case 2:
+    n2 := N(N(N(nil, 3, nil), 4, N(nil, 9, nil)), 20, N(nil, 26, nil))
+    if P(n2) != "((3 4 9) 20 26)" { t.Fatalf("Got %v", P(n2)) }
+
+    expectPut(n2, 15, "((3 4 -) 9 (15 20 26))")
+    expectPut(n2, 8, "((3 4 8) 9 (- 20 26))")
+
+    // Case 2:
+    n3 := N(N(N(N(nil, 2, nil), 3, nil), 4, N(N(nil, 7, nil), 9, N(nil, 11, nil))),
+        20, N(N(nil, 21, nil), 26, N(nil, 30, nil)))
+    if P(n3) != "(((2 3 -) 4 (7 9 11)) 20 (21 26 30))" { t.Fatalf("Got %v", P(n3)) }
+
+    expectPut(n3, 15, "(((2 3 -) 4 7) 9 ((- 11 15) 20 (21 26 30)))")
+    expectPut(n3, 8, "(((2 3 -) 4 (- 7 8)) 9 (11 20 (21 26 30)))")
+
+
+    //////// Test Remove cases:
+
+    // Case 4:
+    n4 := N(N(nil, 1, nil), 2, N(N(nil, 3, nil), 4, N(nil, 5, nil)))
+    if P(n4) != "(1 2 (3 4 5))" { t.Fatalf("Got %v", P(n4)) }
+
+    expectRemove(n4, 1, "((- 2 3) 4 5)")
+
+    // Case 5:
+    n5 := N(N(N(nil, 1, nil), 2, N(N(nil, 3, nil), 4, N(nil, 5, nil))), 6,
+            N(N(N(nil, 7, nil), 8, nil), 9, N(N(nil, 10, nil), 11, N(nil, 12, N(nil, 13, nil)))))
+    if P(n5) != "((1 2 (3 4 5)) 6 ((7 8 -) 9 (10 11 (- 12 13))))" { t.Fatalf("Got %v", P(n5)) }
+
+    expectRemove(n5, 1, "(((- 2 3) 4 5) 6 ((7 8 -) 9 (10 11 (- 12 13))))")
+
+    // Case 6:
+    n6 := N(N(N(nil, 1, nil), 2, N(nil, 3, N(nil, 4, nil))), 5,
+            N(N(N(nil, 6, nil), 7, nil), 8, N(N(nil, 9, nil), 10, N(nil, 11, N(nil, 12, nil)))))
+    if P(n6) != "((1 2 (- 3 4)) 5 ((6 7 -) 8 (9 10 (- 11 12))))" { t.Fatalf("Got %v", P(n6)) }
+
+    expectRemove(n6, 1, "(((2 3 4) 5 (6 7 -)) 8 (9 10 (- 11 12)))")
+
 }
diff --git a/merkle/types.go b/merkle/types.go
index 606b0f037..a7bb33ee9 100644
--- a/merkle/types.go
+++ b/merkle/types.go
@@ -29,6 +29,9 @@ type Node interface {
     Size() int
     Has(key Sortable) bool
     Get(key Sortable) (value interface{}, err error)
+
+    Put(key Sortable, value interface{}) (_ *IAVLNode, updated bool)
+    Remove(key Sortable) (_ *IAVLNode, value interface{}, err error)
 }
 
 type NodeIterator func() (node Node, next NodeIterator)
diff --git a/merkle/tree.go b/merkle/util.go
similarity index 58%
rename from merkle/tree.go
rename to merkle/util.go
index e694e6f02..b4871645d 100644
--- a/merkle/tree.go
+++ b/merkle/util.go
@@ -1,5 +1,9 @@
 package merkle
 
+import (
+    "fmt"
+)
+
 func Iterator(node Node) NodeIterator {
     stack := make([]Node, 0, 10)
     var cur Node = node
@@ -28,3 +32,23 @@ func pop(stack []Node) ([]Node, Node) {
         return stack[0:len(stack)-1], stack[len(stack)-1]
     }
 }
+
+func PrintIAVLNode(node *IAVLNode) {
+    fmt.Println("==== NODE")
+    printIAVLNode(node, 0)
+    fmt.Println("==== END")
+}
+
+func printIAVLNode(node *IAVLNode, indent int) {
+    indentPrefix := ""
+    for i:=0; i<indent; i++ {
+        indentPrefix += "    "
+    }
+    if node == nil {
+        fmt.Printf("%s--\n", indentPrefix)
+    } else {
+        printIAVLNode(node.left, indent+1)
+        fmt.Printf("%s%v:%v\n", indentPrefix, node.key, node.height)
+        printIAVLNode(node.right, indent+1)
+    }
+}