procedural mesh error in triangulation

Hello! I am generating a procedural system, in question everything is fine, but I find a mathematical error in the triangulation, and I can not find the solution, maybe someone with a better eye and understanding can help me ... according to the triangulation int list, it should be like this: 0,1,3 - 3,2,0 | 2,3,5 - 5,2,2 | 4.5.1 - 1.0.4. but the error is in the last row, I do not understand why it remains (4,5,7 - 7,6,4.). I attach an image.

![alt text][1]

I do not understand why it happens to 7, when it should be 1, and to 6 when it should be 0. somebody help me? public GameObject node;

     public Material mat;
     [HideInInspector]
     public GameObject pointDown;
     [HideInInspector]
     public GameObject pointUp;
     [HideInInspector]
     public GameObject pointUpPos;
 
     public GameObject[] pointsDown;
 
     public Vector3[] vertex;
 
     [Range(1,20)]
     public float Height=3;
 
     public int point;
     public int[] triangles;
 
     private int p1;
     private int p2;
     private int p3;
     private int b;
     private int p0;
 
     private float LastComparator;
 
     Ray ray;
     RaycastHit hit;
     public Mesh mesh;
     public MeshFilter mf;
     public MeshRenderer meshrend;
     vertexEditor vertexEdit;
     private int x;
     public int n;
     public float textureScale;
     public bool Create=false;
     public int change;
 
     void Start () {
 
         Height = 3;
         mat = Resources.Load ("fence", typeof (Material)) as Material;
         mat.mainTextureScale = new Vector2(1,1);
         mesh = new Mesh ();
         meshrend = this.gameObject.AddComponent<MeshRenderer> ();
         meshrend.material = mat;
         mf = this.gameObject.AddComponent<MeshFilter> ();
         textureScale=1;
     }
 
     public void GenMesh(){
 
         b = -4;
         p1 = b + 2;
         p2 = p1 + 1;
         p3 = p2 + 2;
         p0 = -1;
 
         for (n = 0; n < triangles.Length; n+=change) {
 
             b = x - 2;
             p1 += 2;
             p2 += 2;
             p3 += 2;
 
             triangles [n] = p1;
             triangles [n + 1] = p2;
             triangles [n + 2] = p3;
 
             triangles [n + 3] = p3;
             triangles [n + 4] = p3 - 1;
             triangles [n + 5] = p1;
 
             triangles [n + 6] = p3-1;
             triangles [n + 7] = p3;
             triangles [n + 8] = 1;
 
             triangles [n + 9] = 1;
             triangles [n + 10] = p0 +1;
             triangles [n + 11] = p3-1;
             mesh.triangles = triangles;
         }
     }
 
 
     void Update () {
 
 
         mesh.Clear ();
         mesh.vertices = vertex;
         mf.mesh = mesh;
         point = pointsDown.Length;
 
         pointsDown = GameObject.FindGameObjectsWithTag ("vertex");
         vertex = new Vector3[pointsDown.Length];
 
 
         for (x = 0; x < pointsDown.Length; x++) {
         
             vertex[x] = new Vector3(pointsDown[x].transform.position.x,pointsDown[x].transform.position.y,pointsDown[x].transform.position.z);
         }
 
         if (point > 0) {
             change = 3;
             triangles = new int[pointsDown.Length/2*3];
         }
 
         if (point > 4) {
             triangles = new int[pointsDown.Length *3];
             change = 6;
             GenMesh ();
         }
 
         // uvmap area.
         Vector2[] uvs = new Vector2[vertex.Length];
 
         for (int i = 0; i < vertex.Length; i++)
               {
             
             Vector3 uvpos = new Vector3(vertex[i].x, ((vertex[i].x) + (vertex[i].z)), vertex[i].z);
             Vector3 direction = uvpos / uvpos.magnitude;
 
                uvs[i] = new Vector2(((vertex[i].x * direction.x) + (vertex[i].z * direction.z)) / 1, vertex[i].y / 1);
 
               }
 
         mesh.uv = uvs;
 
     }
 }