About forty publishers from various parts of the country are taking part in the 13th National Book Fair, opened Saturday in Biskra (425 km southeast of Algiers) by Minister of Religious Affairs Bouabdallah Ghlamallah. The minister, visiting the different stands of the fair, organized every year in the province, made a long stop at the pavilion displaying the books published by the his ministerial department.   The event, to run until mid-March, displays more than 1,500 titles about various fields, including religion, science and technology, dictionaries, encyclopaedias and children's books. According to the head of the national union of book publishers, Ahmed Madi, the cultural event is intended to present the most recently published books to university students, academics, researchers as well as all sorts of readers.