Generic invariance

Norm parameterized types are invariant. List<Circle> and List<Shape> are distinct types and cannot be assigned directly to each other; nullability does not change this rule.

The existential projection ? hides one existing type argument. Reading a method result that is the hidden parameter uses its declared upper bound, or Any? when unconstrained, and preserves declared nullability. Nested arguments remain projected: reading List<T> produces List<?>, not List<Any?>.