12. For the purposes of this act, only the following books are to be taken into consideration:(a) non-periodical printed publications having not less than 49 pages of text or illustrations or both, excluding covers, however collated;
(b) non-periodical printed publications for children, having not less than 16 pages, bound in paper covers or in hard covers, with text or illustrations or both, or in the form of comic strips with or without text;
(c) non-periodical printed publications in the form of comic strips for adults, having not less than 16 pages, with text, bound in paper covers or hard covers;
(d) non-periodical printed publications dealing solely with music, bound in paper covers or hard covers, having any number of pages, as well as instrumental method and musical scores;
(e) serial publications, namely publications complying with one of the above paragraphs a to d, comprising several parts or volumes published successively under a general title over an indeterminate period but not necessarily at regular intervals.