diff --git a/sympde/core/algebra.py b/sympde/core/algebra.py
index 7b626117..bd2513d1 100644
--- a/sympde/core/algebra.py
+++ b/sympde/core/algebra.py
@@ -274,48 +274,32 @@ def __new__(cls, *args, **options):
         else:
             return r
 
-class Inner_2d(InnerBasic):
-
     @classmethod
     def eval(cls, *_args):
-        """."""
 
         if not _args:
             return
 
-        if not( len(_args) == 2):
+        if len(_args) != 2:
             raise ValueError('Expecting two arguments')
 
-        u = _args[0]
-        v = _args[1]
+        u, v = _args
 
         u = Matrix(u)
         v = Matrix(v)
 
         # TODO add conjugate
-        M = u.transpose()*v
+        M = u.transpose() * v
         return M.trace()
 
+# ...
+class Inner_1d(InnerBasic):
+    pass
 
-class Inner_3d(InnerBasic):
-
-    @classmethod
-    def eval(cls, *_args):
-        """."""
-
-        if not _args:
-            return
-
-        if not( len(_args) == 2):
-            raise ValueError('Expecting two arguments')
-
-        u = _args[0]
-        v = _args[1]
-
-        u = Matrix(u)
-        v = Matrix(v)
+# ...
+class Inner_2d(InnerBasic):
+    pass
 
-        # TODO add conjugate
-        M = u.transpose()*v
-        return M.trace()
 # ...
+class Inner_3d(InnerBasic):
+    pass
diff --git a/sympde/expr/evaluation.py b/sympde/expr/evaluation.py
index 9edda70a..85dbb039 100644
--- a/sympde/expr/evaluation.py
+++ b/sympde/expr/evaluation.py
@@ -16,7 +16,7 @@
 
 from sympde.core.basic import _coeffs_registery
 from sympde.core.basic import CalculusFunction
-from sympde.core.algebra import (Dot_1d,
+from sympde.core.algebra import (Dot_1d, Inner_1d,
                                  Dot_2d, Inner_2d, Cross_2d,
                                  Dot_3d, Inner_3d, Cross_3d)
 from sympde.core.utils import random_string