Hi Lawrence, I had already tried this based on examples from firedrake/utility_meshes.py, but I get the following error: Traceback (most recent call last): File "mesh.py", line 39, in <module> V = FunctionSpace(mesh, "CG", 1) File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/functionspace.py", line 636, in __new__ mesh.init() File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/mesh.py", line 750, in init self._callback(self) File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/mesh.py", line 1040, in callback dim=geometric_dim) File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/functionspace.py", line 695, in __new__ self = super(VectorFunctionSpace, cls).__new__(cls, mesh_t, element, name=name, shape=(dim,)) File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/functionspace.py", line 140, in __new__ dmplex.get_facet_nodes(mesh.exterior_facets.facet_cell, File "/Users/matak/firedrake/lib/python2.7/site-packages/pyop2/utils.py", line 64, in __get__ obj.__dict__[self.__name__] = result = self.fget(obj) File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/mesh.py", line 471, in exterior_facets boundary_ids, unique_markers=unique_ids) File "/Users/matak/firedrake/lib/python2.7/site-packages/firedrake/mesh.py", line 61, in __init__ "Every marker has to be contained in unique_markers" AssertionError: Every marker has to be contained in unique_markers A sample code can be found attached. Best, Anna.