Use case Actor generalization

Is my use case diagram correct ?

I need help to know if my use case diagram is correct or not, and if the actor admin inherits from manager, and manager inherits from technician, does that mean the generalization between admin and technician is unnecessary and can be done through the relation between manager and technician?

The generalizations in your diagram means that:

• Manager -|> Technician : every instance of Manager is also an instance of Technician.
• Admin -|> Manager : every instance of Admin is also an instance of Manager.

This implies that every instance of Admin is also an instance of Technician, i.e that Technician is also a generalization of Admin.

Your direct inheritance between Admin and Technician is therefore redundant. It is not wrong, but considering that multiple inheritance make some people unconfortable, I'd suggest to avoid it.