diff --git a/avl/avl_test.go b/avl/avl_test.go
index 8c28b38..b412a4d 100644
--- a/avl/avl_test.go
+++ b/avl/avl_test.go
@@ -252,12 +252,12 @@ ALL:
 	}
 }
 
-const PutCompartorSize = 300000
+const CompartorSize = 300000
 const NumberMax = 60000000
 
 func BenchmarkIterator(b *testing.B) {
 	avl := New(utils.IntComparator)
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 
 	for i := 0; i < b.N; i++ {
 		v := randomdata.Number(0, NumberMax)
@@ -283,7 +283,7 @@ func BenchmarkIterator(b *testing.B) {
 
 func BenchmarkGodsIterator(b *testing.B) {
 	avl := avltree.NewWithIntComparator()
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 
 	for i := 0; i < b.N; i++ {
 		v := randomdata.Number(0, NumberMax)
@@ -310,7 +310,7 @@ func BenchmarkGodsIterator(b *testing.B) {
 func BenchmarkRemove(b *testing.B) {
 
 	avl := New(utils.IntComparator)
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 
 	var l []int
 	for i := 0; i < b.N; i++ {
@@ -329,7 +329,7 @@ func BenchmarkRemove(b *testing.B) {
 
 func BenchmarkGodsRemove(b *testing.B) {
 	avl := avltree.NewWithIntComparator()
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 
 	var l []int
 	for i := 0; i < b.N; i++ {
@@ -349,7 +349,7 @@ func BenchmarkGodsRemove(b *testing.B) {
 func BenchmarkGet(b *testing.B) {
 	avl := New(utils.IntComparator)
 
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 	for i := 0; i < b.N/2; i++ {
 		avl.Put(randomdata.Number(0, NumberMax))
 	}
@@ -364,7 +364,7 @@ func BenchmarkGet(b *testing.B) {
 func BenchmarkGodsRBGet(b *testing.B) {
 	rb := redblacktree.NewWithIntComparator()
 
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 	for i := 0; i < b.N/2; i++ {
 		rb.Put(randomdata.Number(0, NumberMax), i)
 	}
@@ -379,7 +379,7 @@ func BenchmarkGodsRBGet(b *testing.B) {
 func BenchmarkGodsAvlGet(b *testing.B) {
 	rb := avltree.NewWithIntComparator()
 
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 	for i := 0; i < b.N/2; i++ {
 		rb.Put(randomdata.Number(0, NumberMax), i)
 	}
@@ -400,7 +400,7 @@ func BenchmarkPut(b *testing.B) {
 
 	b.ResetTimer()
 	b.StartTimer()
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 	for i := 0; i < b.N; i++ {
 		avl.Put(randomdata.Number(0, NumberMax))
 	}
@@ -417,7 +417,7 @@ func BenchmarkGodsRBPut(b *testing.B) {
 	b.ResetTimer()
 	b.StartTimer()
 
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 	for i := 0; i < b.N; i++ {
 		rb.Put(randomdata.Number(0, NumberMax), i)
 	}
@@ -434,7 +434,7 @@ func BenchmarkGodsPut(b *testing.B) {
 	b.ResetTimer()
 	b.StartTimer()
 
-	b.N = PutCompartorSize
+	b.N = CompartorSize
 	for i := 0; i < b.N; i++ {
 		avl.Put(randomdata.Number(0, NumberMax), i)
 	}
diff --git a/avl/iterator.go b/avl/iterator.go
index 872d67f..1ca8d57 100644
--- a/avl/iterator.go
+++ b/avl/iterator.go
@@ -1,7 +1,7 @@
 package avl
 
 import (
-	"github.com/emirpasic/gods/stacks/arraystack"
+	"474420502.top/eson/structure/lastack"
 )
 
 type Iterator struct {
@@ -10,12 +10,12 @@ type Iterator struct {
 	dir    int
 	up     *Node
 	cur    *Node
-	tstack *arraystack.Stack
+	tstack *lastack.Stack
 	// curnext *Node
 }
 
 func initIterator(avltree *AVL) *Iterator {
-	iter := &Iterator{op: avltree, tstack: arraystack.New()}
+	iter := &Iterator{op: avltree, tstack: lastack.New()}
 	iter.up = avltree.root
 	return iter
 }
diff --git a/interface.go b/interface.go
new file mode 100644
index 0000000..a80b419
--- /dev/null
+++ b/interface.go
@@ -0,0 +1,9 @@
+package structure
+
+type IteratorNext interface {
+	Next() bool
+}
+
+type IteratorPrev interface {
+	Prev() bool
+}