unexpected symbol

Im trying to build a tetris game however the script will not work. it keeps saying unexpected symbol "bool" on line 18 and i do not know how to fix it.

 using UnityEngine;
 using System.Collections;
 
 public class Grid : MonoBehaviour {
     // The Grid itself
     public static int w = 10;
     public static int h = 20;
     public static Transform[,] grid = new Transform[w, h];
 }
 
 public class Vector2 : MonoBehaviour 
 {
 public static Vector2 roundVec2(Vector2 v) {
     return new Vector2(Mathf.Round(v.x),
         Mathf.Round(v.y));
     }
 }
 public static bool insideBorder(Vector2 pos)
     {
     return ((int)pos.x >= 0 &&
         (int)pos.x < w &&
         (int)pos.y >= 0);
 }
 public static void deleteRow(int y) {
     for (int x = 0; x < w; ++x) {
         Destroy(grid[x, y].gameObject);
         grid[x, y] = null;
     }
 }
 public static void decreaseRow(int y) {
     for (int x = 0; x < w; ++x) {
         if (grid[x, y] != null) {
             // Move one towards bottom
             grid[x, y-1] = grid[x, y];
             grid[x, y] = null;
 
             // Update Block position
             grid[x, y-1].position += new Vector3(0, -1, 0);
         }
     }
 }
 public static void deleteFullRows() {
     for (int y = 0; y < h; ++y) {
         if (isRowFull(y)) {
             deleteRow(y);
             decreaseRowsAbove(y+1);
             --y;
         }
     }
 }
 bool isValidGridPos() {        
     foreach (Transform child in transform) {
         Vector2 v = Grid.roundVec2(child.position);
 
         // Not inside Border?
         if (!Grid.insideBorder(v))
             return false;
 
         // Block in grid cell (and not part of same group)?
         if (Grid.grid[(int)v.x, (int)v.y] != null &&
             Grid.grid[(int)v.x, (int)v.y].parent != transform)
             return false;
     }
     return true;
 }
 oid updateGrid() {
     // Remove old children from grid
     for (int y = 0; y < Grid.h; ++y)
         for (int x = 0; x < Grid.w; ++x)
             if (Grid.grid[x, y] != null)
             if (Grid.grid[x, y].parent == transform)
                 Grid.grid[x, y] = null;
 
     // Add new children to grid
     foreach (Transform child in transform) {
         Vector2 v = Grid.roundVec2(child.position);
         Grid.grid[(int)v.x, (int)v.y] = child;
     }        
 }
 void Update() {
     // Move Left
     if (Input.GetKeyDown(KeyCode.LeftArrow)) {
         // Modify position
         transform.position += new Vector3(-1, 0, 0);
 
         // See if valid
         if (isValidGridPos())
             // Its valid. Update grid.
             updateGrid();
         else
             // Its not valid. revert.
             transform.position += new Vector3(1, 0, 0);
     }
 }
 else if (Input.GetKeyDown(KeyCode.RightArrow)) {
     // Modify position
     transform.position += new Vector3(1, 0, 0);
 
     // See if valid
     if (isValidGridPos())
         // It's valid. Update grid.
         updateGrid();
     else
         // It's not valid. revert.
         transform.position += new Vector3(-1, 0, 0);
 }
 else if (Input.GetKeyDown(KeyCode.UpArrow)) {
     transform.Rotate(0, 0, -90);
 
     // See if valid
     if (isValidGridPos())
         // It's valid. Update grid.
         updateGrid();
     else
         // It's not valid. revert.
         transform.Rotate(0, 0, 90);
 }
 else if (Input.GetKeyDown(KeyCode.DownArrow)) {
     // Modify position
     transform.position += new Vector3(0, -1, 0);
 
     // See if valid
     if (isValidGridPos()) {
         // It's valid. Update grid.
         updateGrid();
     } else {
         // It's not valid. revert.
         transform.position += new Vector3(0, 1, 0);
 
         // Clear filled horizontal lines
         Grid.deleteFullRows();
 
         // Spawn next Group
         FindObjectOfType<Spawner>().spawnNext();
 
         // Disable script
         enabled = false;
     }
 }
 float lastFall = 0;
 else if (Input.GetKeyDown(KeyCode.DownArrow) ||
     Time.time - lastFall >= 1) {
     // Modify position
     transform.position += new Vector3(0, -1, 0);
 
     // See if valid
     if (isValidGridPos()) {
         // It's valid. Update grid.
         updateGrid();
     } else {
         // It's not valid. revert.
         transform.position += new Vector3(0, 1, 0);
 
         // Clear filled horizontal lines
         Grid.deleteFullRows();
 
         // Spawn next Group
         FindObjectOfType<Spawner>().spawnNext();
 
         // Disable script
         enabled = false;
     }
 
     lastFall = Time.time;
 }
 void Update() {
     // Move Left
     if (Input.GetKeyDown(KeyCode.LeftArrow)) {
         // Modify position
         transform.position += new Vector3(-1, 0, 0);
 
         // See if valid
         if (isValidGridPos())
             // It's valid. Update grid.
             updateGrid();
         else
             // It's not valid. revert.
             transform.position += new Vector3(1, 0, 0);
     }
 
     // Move Right
     else if (Input.GetKeyDown(KeyCode.RightArrow)) {
         // Modify position
         transform.position += new Vector3(1, 0, 0);
 
         // See if valid
         if (isValidGridPos())
             // It's valid. Update grid.
             updateGrid();
         else
             // It's not valid. revert.
             transform.position += new Vector3(-1, 0, 0);
     }
 
     // Rotate
     else if (Input.GetKeyDown(KeyCode.UpArrow)) {
         transform.Rotate(0, 0, -90);
 
         // See if valid
         if (isValidGridPos())
             // It's valid. Update grid.
             updateGrid();
         else
             // It's not valid. revert.
             transform.Rotate(0, 0, 90);
     }
 
     // Move Downwards and Fall
     else if (Input.GetKeyDown(KeyCode.DownArrow) ||
         Time.time - lastFall >= 1) {
         // Modify position
         transform.position += new Vector3(0, -1, 0);
         void Start() {
             // Default position not valid? Then it's game over
             if (!isValidGridPos()) {
                 Debug.Log("GAME OVER");
                 Destroy(gameObject);
             }
         }
 
 
         // See if valid
         if (isValidGridPos()) {
             // It's valid. Update grid.
             updateGrid();
         } else {
             // It's not valid. revert.
             transform.position += new Vector3(0, 1, 0);
 
             // Clear filled horizontal lines
             Grid.deleteFullRows();
 
             // Spawn next Group
             FindObjectOfType<Spawner>().spawnNext();
 
             // Disable script
             enabled = false;
         }
 
         lastFall = Time.time;
     }
 }