diff --git a/examples/01_simple_type_checking/04_complex_types.midas b/examples/01_simple_type_checking/04_complex_types.midas
index b920c37..b561cef 100644
--- a/examples/01_simple_type_checking/04_complex_types.midas
+++ b/examples/01_simple_type_checking/04_complex_types.midas
@@ -1,11 +1,21 @@
 type Meter = float
 
 extend Meter {
-    op __add__(Meter) -> Meter
-    op __sub__(Meter) -> Meter
+    def __add__: fn(Meter) -> Meter
+    def __sub__: fn(Meter) -> Meter
 }
 
-type Coordinate = {
-    x: Meter
-    y: Meter
+type Coordinate = object
+
+extend Coordinate {
+    prop x: Meter
+    prop y: Meter
+}
+
+type Difference[T <: float] = T
+type MeterDifference = Difference[Meter]
+
+type CompDiff[T <: float] = {
+    prop d1: Difference[T]
+    prop d2: Difference[T]
 }
\ No newline at end of file
diff --git a/examples/01_simple_type_checking/04_complex_types.py b/examples/01_simple_type_checking/04_complex_types.py
index 63fd1e7..ebe958f 100644
--- a/examples/01_simple_type_checking/04_complex_types.py
+++ b/examples/01_simple_type_checking/04_complex_types.py
@@ -1,5 +1,6 @@
 # type: ignore
 # ruff: disable [F821]
+
 p1: Coordinate
 p2: Coordinate
 
@@ -9,6 +10,21 @@ diff_y = p2.y - p1.y
 dist = diff_x + diff_y
 
 p2.x += cast(Meter, 1)
-p2.y = True
-p2.z = 3
-p2.x.a = 3
+p2.y = True  # invalid, wrong type
+p2.z = 3  # invalid, no property 'z' on Coordinate
+p2.x.a = 3  # invalid, no properties on Meter
+
+foo: list[float] = []
+
+append = foo.append
+
+foo.append("")  # invalid, must be float
+foo.append(2)
+append(True)  # invalid, must be float
+append(2)
+
+bar: list[list[Meter]]
+
+bar.append([p2.x])
+
+foo2 = foo + foo