diff --git a/tree/vbt/iterator.go b/tree/vbt/iterator.go
index 776238b..1bedc99 100644
--- a/tree/vbt/iterator.go
+++ b/tree/vbt/iterator.go
@@ -1,7 +1,7 @@
 package vbt
 
 import (
-	"github.com/474420502/focus/stack/listarraystack"
+	lastack "github.com/474420502/focus/stack/listarraystack"
 )
 
 type Iterator struct {
@@ -112,6 +112,7 @@ func (iter *Iterator) Next() (result bool) {
 
 	return false
 }
+
 func (iter *Iterator) GetPrev(cur *Node, idx int) *Node {
 
 	// iter := NewIterator(cur)
diff --git a/tree/vbt/vbt.go b/tree/vbt/vbt.go
index 29668d0..c574d53 100644
--- a/tree/vbt/vbt.go
+++ b/tree/vbt/vbt.go
@@ -61,7 +61,7 @@ func (tree *Tree) Size() int {
 	return tree.root.size
 }
 
-func (tree *Tree) indexNode(idx int) *Node {
+func (tree *Tree) IndexNode(idx int) *Node {
 	cur := tree.root
 	if idx >= 0 {
 		for cur != nil {
@@ -93,7 +93,7 @@ func (tree *Tree) indexNode(idx int) *Node {
 }
 
 func (tree *Tree) Index(idx int) (interface{}, bool) {
-	n := tree.indexNode(idx)
+	n := tree.IndexNode(idx)
 	if n != nil {
 		return n.value, true
 	}
@@ -117,7 +117,7 @@ func (tree *Tree) IndexRange(idx1, idx2 int) (result []interface{}, ok bool) { /
 			ok = false
 		}
 
-		n := tree.indexNode(idx1)
+		n := tree.IndexNode(idx1)
 		tree.iter.SetNode(n)
 		iter := tree.iter
 		result = make([]interface{}, 0, idx1-idx2)
@@ -139,7 +139,7 @@ func (tree *Tree) IndexRange(idx1, idx2 int) (result []interface{}, ok bool) { /
 			ok = false
 		}
 
-		if n := tree.indexNode(idx1); n != nil {
+		if n := tree.IndexNode(idx1); n != nil {
 			tree.iter.SetNode(n)
 			iter := tree.iter
 			result = make([]interface{}, 0, idx2-idx1)
@@ -161,15 +161,15 @@ func (tree *Tree) IndexRange(idx1, idx2 int) (result []interface{}, ok bool) { /
 }
 
 func (tree *Tree) RemoveIndex(idx int) (interface{}, bool) {
-	n := tree.indexNode(idx)
+	n := tree.IndexNode(idx)
 	if n != nil {
-		tree.removeNode(n)
+		tree.RemoveNode(n)
 		return n.value, true
 	}
 	return nil, false
 }
 
-func (tree *Tree) removeNode(n *Node) {
+func (tree *Tree) RemoveNode(n *Node) {
 	if tree.root.size == 1 {
 		tree.root = nil
 		// return n
@@ -230,7 +230,7 @@ func (tree *Tree) removeNode(n *Node) {
 func (tree *Tree) Remove(key interface{}) (interface{}, bool) {
 
 	if n, ok := tree.GetNode(key); ok {
-		tree.removeNode(n)
+		tree.RemoveNode(n)
 		return n.value, true
 	}
 	// return nil
diff --git a/tree/vbtkey/vbtkey.go b/tree/vbtkey/vbtkey.go
index e5b0459..604b08b 100644
--- a/tree/vbtkey/vbtkey.go
+++ b/tree/vbtkey/vbtkey.go
@@ -62,7 +62,7 @@ func (tree *Tree) Size() int {
 	return tree.root.size
 }
 
-func (tree *Tree) indexNode(idx int) *Node {
+func (tree *Tree) IndexNode(idx int) *Node {
 	cur := tree.root
 	if idx >= 0 {
 		for cur != nil {
@@ -94,7 +94,7 @@ func (tree *Tree) indexNode(idx int) *Node {
 }
 
 func (tree *Tree) Index(idx int) (interface{}, bool) {
-	n := tree.indexNode(idx)
+	n := tree.IndexNode(idx)
 	if n != nil {
 		return n.value, true
 	}
@@ -118,7 +118,7 @@ func (tree *Tree) IndexRange(idx1, idx2 int) (result []interface{}, ok bool) { /
 			ok = false
 		}
 
-		n := tree.indexNode(idx1)
+		n := tree.IndexNode(idx1)
 		tree.iter.SetNode(n)
 		iter := tree.iter
 		result = make([]interface{}, 0, idx1-idx2)
@@ -140,7 +140,7 @@ func (tree *Tree) IndexRange(idx1, idx2 int) (result []interface{}, ok bool) { /
 			ok = false
 		}
 
-		if n := tree.indexNode(idx1); n != nil {
+		if n := tree.IndexNode(idx1); n != nil {
 			tree.iter.SetNode(n)
 			iter := tree.iter
 			result = make([]interface{}, 0, idx2-idx1)
@@ -162,15 +162,15 @@ func (tree *Tree) IndexRange(idx1, idx2 int) (result []interface{}, ok bool) { /
 }
 
 func (tree *Tree) RemoveIndex(idx int) (interface{}, bool) {
-	n := tree.indexNode(idx)
+	n := tree.IndexNode(idx)
 	if n != nil {
-		tree.removeNode(n)
+		tree.RemoveNode(n)
 		return n.value, true
 	}
 	return nil, false
 }
 
-func (tree *Tree) removeNode(n *Node) {
+func (tree *Tree) RemoveNode(n *Node) {
 	if tree.root.size == 1 {
 		tree.root = nil
 		// return n
@@ -231,7 +231,7 @@ func (tree *Tree) removeNode(n *Node) {
 func (tree *Tree) Remove(key interface{}) (interface{}, bool) {
 
 	if n, ok := tree.GetNode(key); ok {
-		tree.removeNode(n)
+		tree.RemoveNode(n)
 		return n.value, true
 	}
 	// return nil
diff --git a/utils/math.go b/utils/math.go
index a66db91..f7c882a 100644
--- a/utils/math.go
+++ b/utils/math.go
@@ -3,6 +3,7 @@ package utils
 var bit = uint(32 << (^uint(0) >> 63))
 var bitsub1 = bit - 1
 
+// AbsInt
 func AbsInt(n int) uint {
 	y := n >> bitsub1
 	return uint((n ^ y) - y)