4 Unavailability of persons
(1) For the purposes of this Act, a person is taken not to be available to give evidence about a fact if-
(a) the person is dead; or
(b) the person is, for any reason other than the application of section 16 (Competence and compellability-judges and jurors), not competent to give the evidence about the fact; or
(c) it would be unlawful for the person to give evidence about the fact; or
(d) a provision of this Act prohibits the evidence being given; or
(e) all reasonable steps have been taken, by the party seeking to prove the person is not available, to find the person or to secure his or her attendance, but without success; or
(f) all reasonable steps have been taken, by the party seeking to prove the person is not available, to compel the person to give the evidence, but without success; or
(g) the person is mentally or physically unable to give evidence and it is not reasonably practicable to overcome that inability.
(2) In all other cases the person is taken to be available to give evidence about the fact.