In Deriscope terminology, a is called abstract when it can have no of its own, i.e. Deriscope Objects of which the true type is not a of the Deriscope Type here.
For example the Deriscope Type is abstract because there can never exist a of which the true type is Tradable and not some other subtype of Tradable.
An abstract Deriscope Type cannot have the function
It may though have other Deriscope Functions