See https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/odata-discussion/5g3mk2A7yG8/tluOLeO2AgAJ
 
What is the expected behavior when an Entity Container extends another Entity Container and there is an Entity Set with the same name in both? 
The spec says: "All children of the “base” entity container are added to the “extending” entity container." and "An entity set is identified by its name, a simple identifier that MUST be unique within its entity container."
 
Does that mean this case is invalid?
 
IIUC, 4.01 adds covariance, i.e., the ability for Structural Types to redeclare Properties defined in the base Structural Type with a subtype. It would be nice if the same were possible for Entity Containers, i.e., if an Entity Container that extends another Entity Container could redeclare Entity Sets with a subtype