Proposed resolution:

Core has clarified that the definition abstract is adequate. Issue withdrawn by submitter. NAD.

I am trying to decide is a pure virtual function is a necessary as well as sufficient requirement to be classified as abstract?

For instance, is the following (non-polymorphic) type considered abstract?

struct abstract {
protected:
 abstract(){}
 abstract( abstract const & ) {}
 ~abstract() {}
};

(Suggested that this may be NAD, with an editorial fix-up from Pete on the core wording to make clear that abstract requires a pure virtual function)