Actually deepcopying all members of DoFSymbol in __deepcopy__.

hog/dof_symbol.py

@@ -14,6 +14,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+from copy import deepcopy
 import sympy as sp
 from hog.function_space import FunctionSpace
 from hog.element_geometry import ElementGeometry
@@ -48,4 +49,9 @@ class DoFSymbol(sp.Symbol):
         return obj
 
     def __deepcopy__(self, memo):
-        return DoFSymbol(self.name, self.function_space, self.dof_id, self.function_id)
+        return DoFSymbol(
+            deepcopy(self.name),
+            deepcopy(self.function_space),
+            deepcopy(self.dof_id),
+            deepcopy(self.function_id),
+        )