The most permanent portion of the work of this council was the series of Ten Rules prepared as a guide and instruction for all ecclesiastics or other authorities who might thereafter be charged with the duty of literary censorship. These Rules were reprinted in nearly all subsequent papal Indexes, while in the Spanish Indexes they formed the basis of the more or less modified Rules promulgated by the inquisitors. Sixtus V (1585) replaced the Tridentine Rules with a new series of regulations, but they were reissued by Clement VIII (1592) with a few additions. They find place in the two Indexes of Leo XIII, 1896 and 1900. _The Ten Rules of the Tridentine Index_[129] I. All books condemned by the supreme pontiffs, or general councils, before the year 1515, and not comprised in the present Index, are, nevertheless, to be considered as condemned. II. The books of heresiarchs, whether of those who broached or disseminated their heresies prior to the year above-mentioned, or of those who have been, or are, the heads or leaders of heretics, as Luther, Zwingli, Calvin, Balthasar, Pacimontanus, Swenchfeld, and others similar, are altogether forbidden, whatever may be their titles or subjects. And the books of other heretics, which treat professedly upon religion, are totally condemned; but those which do not treat upon religion are allowed to be read, after having been examined and approved by Catholic divines by order of the bishops and inquisitors. Those Catholic books also are permitted to be read which have been composed by authors who have afterwards fallen into heresy, or who, after their fall, have returned into the bosom of the Church, provided these have been approved by the theological faculty of some Catholic university, or by the general Inquisition.