Per JDK-6480391 and its update to 4.5.1, "The wildcard ? extends Object is equivalent to the unbounded wildcard ?"

This is a subtle point and easy to overlook in a system that represents these two wildcards differently, so JDK-6480391 also added the following rules for type argument containment:
? extends T <= ?
? super T <= ? extends Object

Another rule should be added, also for clarity:
***? <= ? extends Object***

(Note that 18.2.3 already includes a similar rule for inference involving type argument containment.)