Under the influence of Zhivkov's more liberal cultural policy in the 1960s, artists began to show greater variation and creativity in style while retaining the acceptable subject matter for their work. Many experimented with abstracts and other avant-garde forms, but these works were never selected for public showing or purchase by the museums and other state agencies, which are the only significant patrons. The artist, therefore, is usually forced to divide his efforts between those works that will earn a living and those that will give vent to his creative urge. Although nonrepresentational art is not publicly exhibited, a considerable degree of abstraction became acceptable in the late 1960s. According to observers who have had contact with Bulgarian artists, the public had grown bored with the prescribed style and content of artistic production, and the government could no longer effectively enforce the restrictions. Added to the difficulties of enforcement was the increasing exposure of Bulgarians through tourism to the great variety of contemporary art produced in Western Europe and in some of the other communist countries. The most abstract and avant-garde painter in Bulgaria is Genko Genkov, some of whose paintings hang in the National Gallery in Sofia. Graphic artists have been allowed the greatest freedom for abstraction. By its very nature, graphic art tends to be abstract and stylized. Graphic artists such as Maria Nedkova have succeeded in producing works that are highly regarded both by the government and by the avant-garde intelligentsia. Many graphic artists go back to Bulgarian medieval art for inspiration in theme and style. Pencho Koulekov, for instance, who is highly regarded in Bulgaria, uses the primitive two-dimensional perspective, the simplification of forms, the highlighting of the essential, and the omission of all detail that was characteristic of early miniaturists and icon painters. Until the time of independence, sculpture was represented almost exclusively by decorative wood carvings. With the introduction of Western influences, several artists turned to the use of stone. Few Bulgarian sculptors achieved international fame, however, although the work of some professors of fine arts in Sofia were becoming known outside the country. Among them was the noted woodcut artist, Vasil Zakhariev, and a former director of the Academy of Fine Arts, Ivan Lasarov. The three-dimensional nature of sculpture and the classic Greek tradition of literal representation have made it difficult for contemporary sculptors to break away from the realistic representational requirements of the regime. Only sculptures designed for children's playgrounds and parks are allowed a degree of abstraction characteristic of art created by children themselves. Observers have commented that works considered highly modern in Bulgaria are completely traditional and representational to the Western eye. ARCHITECTURE