In all cases, the sources from which the copying is made and the names of the authors shall be clearly mentioned. Article(18) The heirs of an author shall have exclusive right to determine publishing his works which were not published during his life time, unless the author requests otherwise in his will. However, if the author fixes a date for publication, the work may not be published before that date. Article(19) the heirs of an author shall have exclusive right to exercise the financial utilization rights provided for in this law. If the work is a joint effort and one of the authors dies without leaving an heir or a legatee, his share shall devolve to his partners in the authorship or their successors, unless it is otherwise agreed. Article(20) Without prejudice to the provisions of Article (8), the financial utilization rights provided for in this law shall expire with the elapse of twenty five years after the death of the author, provided that the total period of protection shall not be less than fifty years as from the date of first publication of the work. However, with respect to photographic and cinematic works which are limited to the mere mechanical transmission of scenery, such rights shall expire with the lapse of five years as from the date of first publication of the work. The period of protection for joint works of art shall be calculated as from the date of death of the last author who survived. If the author is a legal public or private entity, the financial utilization rights shall expire with the elapse of thirty years as from the date of first publication of the work. Article(21) The financial utilization rights of works of art published anonymously and under a pseudonym shall expire with the elapse of twenty five years after publication of the work, unless the author's identity is revealed within this period, in which case the protection period shall be calculated according to paragraph one of the previous article. Article(22) Without prejudice to the provisions of paragraph two of Article (20), the protection period for the works of art published for the first time after the author's death shall expire with the elapse of fifty years after his death.