I can not get the zombie to move. Help please

Hello, I am on the first part of chapter 2, pg 60. I am not able to get the zombie to move at all. Can some one tell me if I have the code wrong. I have been stuck on this for hours. I want to figure it out before I move onto the next part.

import SpriteKit

class GameScene: SKScene {

let zombie = SKSpriteNode(imageNamed: "zombie1")

override func didMoveToView(view: SKView) {
    backgroundColor = SKColor.blackColor()
    let background = SKSpriteNode(imageNamed: "background1")
    background.position = CGPoint(x: size.width/2, y: size.height/2)
    background.anchorPoint = CGPoint(x: 0.5, y: 0.5) // Default        
   // background.zRotation = CGFloat (M_PI) / 8
   background.zPosition = -1
    let mySize = background.size
    print("size: \(mySize)")
    let zombie = SKSpriteNode(imageNamed: "zombie1")
    zombie.position = CGPoint(x:400, y: 400)
override func update(currentTime: NSTimeInterval) {
    zombie.position = CGPoint(x: zombie.position.x + 8, y: zombie.position.y)


Figured it out as soon as I posted this, by re-looking at my code. I did not remove the" let zombie = " in the func didMoveToView