How is it shown that only one actor can access an extending use case?

Question

• Use Case A is extended by Use Case B.
• Use Case A can be done by Actor X and Actor Y.

How can I show that Use Case B is accessible only to Actor X and not Y?

For example, in an e-shop:

• "Find Product" is extended by "Add to wishlist".
• "Find Product" can be done by both a Registered and a Non-Registered Actor.

However, "Add to wishlist" use case can only be done by a Registered Actor.

Answer 1

Simply add a constraint like {can only be performed by Actor X} to the use case in question.