4 files changed, 9 insertions, 5 deletions
diff --git a/polymatrix/expression/expression.py b/polymatrix/expression/expression.py
index 2e4d544..e4f2648 100644
--- a/polymatrix/expression/expression.py
+++ b/polymatrix/expression/expression.py
@@ -56,11 +56,11 @@ class Expression(ExpressionBaseMixin, ABC):
         else:
             return attr
 
-    def __getitem__(self, slice: int | slice | tuple[int | slice, int | slice]) -> Expression:
+    def __getitem__(self, item: int | slice | tuple[int | slice, int | slice]) -> Expression:
         return self.copy(
             underlying=init.init_slice_expr(
                 underlying=self.underlying,
-                slice=slice
+                slices=item
             ),
         )
 
diff --git a/polymatrix/expression/init.py b/polymatrix/expression/init.py
index 15557f4..f0c2a0b 100644
--- a/polymatrix/expression/init.py
+++ b/polymatrix/expression/init.py
@@ -392,9 +392,12 @@ def init_shape_expr(underlying: ExpressionBaseMixin):
 
 def init_slice_expr(
     underlying: ExpressionBaseMixin,
-    slice: tuple[int | slice | range, int | slice | range]
+    slices: int | slice | range | tuple[int | slice | range, int | slice | range]
 ):
-    return polymatrix.expression.impl.SliceExprImpl(underlying, slice)
+    # FIXME: For some reason in older python versions slice is not a hashable
+    # type and this causes crashes when old code uses the cache in the state object
+    # cf. https://stackoverflow.com/questions/29980786/why-are-slice-objects-not-hashable-in-python
+    return polymatrix.expression.impl.SliceExprImpl(underlying, slices)
 
 
 
diff --git a/polymatrix/polymatrix/index.py b/polymatrix/polymatrix/index.py
index e4bd7d1..53c63f1 100644
--- a/polymatrix/polymatrix/index.py
+++ b/polymatrix/polymatrix/index.py
@@ -14,7 +14,7 @@ PolynomialMatrixData = dict[tuple[int, int], PolynomialData]
 
 
 class VariableIndex(NamedTuple):
-    """
+    r"""
     Index for a variable raised to an integral power.
 
     `VariableIndex` has a partial order with respect to the variable index. For
diff --git a/polymatrix/polymatrix/init.py b/polymatrix/polymatrix/init.py
index d66a3d0..8b390c4 100644
--- a/polymatrix/polymatrix/init.py
+++ b/polymatrix/polymatrix/init.py
@@ -150,6 +150,7 @@ def to_affine_expression(p: PolyMatrixMixin) -> PolyMatrixAsAffineExpressionMixi
     
     # Generate slices to index sub-matrices
     slices = {
+        # TODO: use range directly without tuple
         m: tuple(range(i*ncols, (i+1)*ncols))
         for i, m in enumerate(monomials)
     }