The converse of the separation of powers is the decision of the High Court in Boilermakers' Case in 1956, that Chapter III courts cannot be invested with anything other than judicial power. To some extent the rigour of the separation of powers doctrine was softened by the Court's subsequent acceptance that judges could, constitutionally, be assigned functions in their personal capacity as judges rather than as members of a Chapter III court. But this raised the question of which such functions were compatible with the simultaneous holding of Federal judicial office. The answers offered by the Court have been controversial and involved some very fine distinctions: for instance, it has held that a power to authorise telephone interceptions is compatible, while a power to make recommendations concerning the protection of land which might be of heritage significance to Aboriginals is not compatible. The most striking application (and extension) of this "incompatibility" doctrine, however, has involved the Supreme Court of the State of New South Wales, a court that may be invested with Federal jurisdiction. Kable v Director of Public Prosecutions (1996) concerned a criminal law passed by the New South Parliament and directed at a single named individual (somewhat in the manner of a Bill of attainder). The individual was a prisoner (under state law) whose sentence was about to expire but who was alleged to have made threats against the safety of various persons, to be carried out when released. The State Parliament enacted a law, applying only to him, which authorised the Supreme Court of New South Wales to make "preventive detention orders" for periods up to six months, with the possibility of renewal. The orders were to be made if the Court was satisfied, "on the balance of probabilities", that the person to whom the Act applied was "more likely than not to commit a serious act of violence". It is clear that, had the Federal Parliament passed such an Act, it would be found invalid, as it was in effect a legislative judgment and so violated of the constitutional separation of the judicial power. However, the High Court found that the separation of powers was not a feature of the New South Wales constitution, so the State Act was not invalid on that ground. The Act was found invalid, however, on the ground that since the Supreme Court of New South Wales had been invested with