diff --git a/ufl/algorithms/compute_form_data.py b/ufl/algorithms/compute_form_data.py
index 79b114a75..ca8189418 100644
--- a/ufl/algorithms/compute_form_data.py
+++ b/ufl/algorithms/compute_form_data.py
@@ -13,9 +13,9 @@
 
 from ufl.utils.sequences import max_degree
 
-from ufl.classes import GeometricFacetQuantity, Coefficient, Form, FunctionSpace
+from ufl.classes import GeometricFacetQuantity, Coefficient, Subspace, Form, FunctionSpace
 from ufl.corealg.traversal import traverse_unique_terminals
-from ufl.algorithms.analysis import extract_coefficients, extract_sub_elements, unique_tuple
+from ufl.algorithms.analysis import extract_coefficients, extract_subspaces, extract_sub_elements, unique_tuple
 from ufl.algorithms.formdata import FormData
 from ufl.algorithms.formtransformations import compute_form_arities
 from ufl.algorithms.check_arities import check_form_arity
@@ -128,7 +128,8 @@ def _compute_form_data_elements(self, arguments, coefficients, subspaces, domain
     #       almost working, with the introduction of the coordinate
     #       elements here.
 
-    all_elements = self.argument_elements + self.coefficient_elements + self.subspace_elements + self.coordinate_elements
+    all_elements = self.argument_elements + self.coefficient_elements + \
+        self.subspace_elements + self.coordinate_elements
     all_sub_elements = extract_sub_elements(all_elements)
 
     self.unique_elements = unique_tuple(all_elements)
@@ -175,7 +176,7 @@ def _build_object_replace_map(objects, element_mapping=None):
     elif all(isinstance(o, Subspace) for o in objects):
         object_type = Subspace
     else:
-        raise ValueError(f"objects must either be all Coefficents or Subspaces.")
+        raise ValueError("objects must either be all Coefficents or Subspaces.")
     if element_mapping is None:
         element_mapping = {}
 
@@ -194,7 +195,7 @@ def _build_object_replace_map(objects, element_mapping=None):
         new_objects.append(new_f)
         replace_map[f] = new_f
 
-    return new_coefficients, replace_map
+    return new_objects, replace_map
 
 
 def attach_estimated_degrees(form):
diff --git a/ufl/algorithms/strip_terminal_data.py b/ufl/algorithms/strip_terminal_data.py
index aeee48c54..543c34efd 100644
--- a/ufl/algorithms/strip_terminal_data.py
+++ b/ufl/algorithms/strip_terminal_data.py
@@ -28,7 +28,7 @@ def coefficient(self, o):
 
     def subspace(self, o):
         o_new = Subspace(strip_function_space(o.ufl_function_space()),
-                            o.count())
+                         o.count())
         return self.mapping.setdefault(o, o_new)
 
     def constant(self, o):
@@ -123,4 +123,4 @@ def strip_domain(domain):
         meshes = [strip_domain(mesh) for mesh in domain.ufl_meshes()]
         return TensorProductMesh(meshes, domain.ufl_id())
     else:
-        raise NotImplemen`tedError(f"{type(domain)} cannot be stripped")
+        raise NotImplementedError(f"{type(domain)} cannot be stripped")
diff --git a/ufl/projected.py b/ufl/projected.py
index 5349cfe35..6c0244d9c 100644
--- a/ufl/projected.py
+++ b/ufl/projected.py
@@ -3,6 +3,7 @@
 
 from ufl.constantvalue import Zero
 from ufl.core.ufl_type import ufl_type
+from ufl.core.expr import Expr, ufl_err_str
 from ufl.core.operator import Operator
 from ufl.subspace import Subspace
 from ufl.precedence import parstr
diff --git a/ufl/subspace.py b/ufl/subspace.py
index 6befd3966..a706e5123 100644
--- a/ufl/subspace.py
+++ b/ufl/subspace.py
@@ -5,11 +5,8 @@
 from ufl.core.terminal import Terminal
 from ufl.finiteelement import FiniteElementBase
 from ufl.domain import default_domain
-from ufl.functionspace import AbstractFunctionSpace, FunctionSpace, MixedFunctionSpace
-from ufl.form import BaseForm
-from ufl.split_functions import split
+from ufl.functionspace import AbstractFunctionSpace, FunctionSpace
 from ufl.utils.counted import Counted
-from ufl.duals import is_primal, is_dual
 
 # --- The Subspace class represents a subspace in a form ---