Dear Community,

I understand that the faces have to be the same for periodic boundary conditions, but I also would like to use an unstructured mesh. Does anyone know how I can accomplish this? The code below is what does not work at the moment.

```
// build an unstructured mesh for the cube
// run in terminal with FreeFEM++ unstrucCubeMesh.edp
load "distance"
load "msh3"
load "tetgen"
load "medit"
load "mshmet"
load "iovtk"
include "Cube.idp"
int[int] NN = [10,10,10]; //the number of step in each direction
real [int, int] BB = [[0,1],[0,1],[0,1]]; //the bounding box
int [int, int] LB = [[1,2],[3,4],[5,6]]; //the label of the 6 face left,right, front, back, down, right
mesh3 Th = Cube(NN, BB, LB);
medit("Th", Th);
real L = 1.;
int meshSize = 30.;
real[int] domain = [0, 0, 0, 0, 1];
Th = tetgreconstruction(Th, switch = "raAQ", regionlist = domain, sizeofvolume = (L*1./meshSize)^3/6);
medit("Th", Th);
fespace Vh(Th, P1, periodic = [[5, x, y], [6, x, y]]); // periodic boundary conditions on z = 0, 1
```