diff --git a/midas/checker/frames/frame_manager.py b/midas/checker/frames/frame_manager.py
index 74db171..72146b3 100644
--- a/midas/checker/frames/frame_manager.py
+++ b/midas/checker/frames/frame_manager.py
@@ -232,7 +232,7 @@ class FrameManager:
             if col.name == name:
                 index = i
                 replace = True
-                # TODO: check column type here to prevent changing it
+                # TODO: might want to check column type here to disallow changing it
             new_columns.append(col)
 
         new_col: DataFrameType.Column = DataFrameType.Column(
diff --git a/midas/checker/python.py b/midas/checker/python.py
index ef8e688..cb67492 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -454,7 +454,6 @@ class PythonTyper(
         self.env.define(stmt.name, function)
 
     def visit_type_assign(self, stmt: p.TypeAssign) -> None:
-        # TODO check not yet defined locally
         type: Type = self.resolve_type_expr(stmt.type)
         self.env.define(stmt.name, type)
 
@@ -844,7 +843,7 @@ class PythonTyper(
     def visit_ternary_expr(self, expr: p.TernaryExpr) -> Type:
         test_type: Type = self.type_of(expr.test)
 
-        # TODO Allow subtypes or any type
+        # Strict: test must be a subtype of bool, or UnknownType
         if (
             not self.is_subtype(test_type, self.types.get_type("bool"))
             and test_type != UnknownType()
@@ -1154,8 +1153,9 @@ class PythonTyper(
                         return False, None
 
                     if key is None:
-                        # TODO: check that value is always a dict
-                        assert isinstance(value_val, dict)
+                        # If literal value is not a dict, invalid Python -> abort
+                        if not isinstance(value_val, dict):
+                            return False, None
                         pairs.extend(value_val.items())
                     else:
                         pairs.append((key_val, value_val))
@@ -1281,9 +1281,7 @@ class PythonTyper(
 
             case BaseType():
                 # TODO: do we want to allow cast(float, int)? would require runtime conversion
-                if not self.types.is_subtype(
-                    subject_type, target_type
-                ) or not self.types.is_subtype(target_type, subject_type):
+                if not self.types.are_equivalent(subject_type, target_type):
                     self.reporter.error(
                         expr.location,
                         f"Value {lit_value!r} of type {subject_type} cannot be cast as {target_type}",
diff --git a/midas/checker/registry.py b/midas/checker/registry.py
index 0c97074..3ce265e 100644
--- a/midas/checker/registry.py
+++ b/midas/checker/registry.py
@@ -213,7 +213,6 @@ class TypesRegistry:
                 return True
 
             case (ColumnType(type=inner1), ColumnType(type=inner2)):
-                # TODO: invariant, replace ColumnType with simple GenericType
                 if not self.are_equivalent(inner1, inner2):
                     return False
                 return True
diff --git a/midas/generator/generator.py b/midas/generator/generator.py
index 08edda7..3cf2423 100644
--- a/midas/generator/generator.py
+++ b/midas/generator/generator.py
@@ -354,7 +354,6 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
         )
 
     def visit_type_assign(self, stmt: p.TypeAssign) -> ast.stmt:
-        # TODO: is that ok?
         return ast.Pass()
 
     def visit_assign_stmt(self, stmt: p.AssignStmt) -> ast.stmt:
diff --git a/midas/generator/stubs.py b/midas/generator/stubs.py
index b228916..1875f93 100644
--- a/midas/generator/stubs.py
+++ b/midas/generator/stubs.py
@@ -53,7 +53,7 @@ class StubsGenerator:
         self.import_pandas = False
         for name, type in self.types._types.items():
             # Skip builtin types, not just based on name so the user can override
-            # TODO: check if added members on builtin type
+            # TODO: check if added members on builtin type, or prevent it
             match type:
                 case BaseType(name=name_) if name == name_:
                     continue
@@ -105,7 +105,9 @@ class StubsGenerator:
         """
         base_type: Type = type
 
-        # TODO: improve
+        # Generate simple assignment for type aliases
+        # A type alias will have a name that is different from the type represents
+        # or will neither be a `DeriveType` nor a `GenericType`
         match type:
             case DerivedType(name=name_) | GenericType(name=name_) if name_ == name:
                 pass