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Well it would have been nice if he stated his interpretation of the Liskov Substitution Principle. The way i understood it best was here [1].

A subclass should behave in a way that it never cause problems when it is used instead of the base class.

In concrete terms:

* No new exceptions are allowed to be thrown, unless they are subtypes of the exception thrown by the base class

* Preconditions cannot be strengthend by the subtype

* Postconditions cannot be weakened by the subtype

For me it is really the focus of using inheritance only if you want substitutability. Otherwise go with composition.

=== [1] https://youtu.be/8ZJ8BVlDIQ4?t=1762

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