A virtual member function is used if it is not pure?

Question

C++03 3.2.2 ...An object or non-overloaded function is used if its name appears in a potentially-evaluated expression. A virtual member function is used

Answer 1

The two clauses are not mutually exclusive. That a virtual function is used if it is not pure, does not mean that the converse holds. If a virtual function is pure it does not mean that it is necessarily not used. It may still be used "if its name appears in a potentially evaluated expression" such as in your example: A::f();.