The axiom of foundation established that every set can be constructed from the bottom up in an ordered succession of steps by way of the principles of Zermelo and Fraenkel, in such a manner that if one set belongs to another then the first must necessarily come before the second in the succession, hence excluding the possibility of a set belonging to itself. To demonstrate that the addition of this new axiom to the others did not produce contradictions, von Neumann introduced a method of demonstration, called the method of inner models, which later became an essential instrument in set theory.
What excluded a set from belonging to itself in set theory?
if one set belongs to another then the first must necessarily come before the second in the succession

Architects such as Frank Lloyd Wright developed Organic architecture, in which the form was defined by its environment and purpose, with an aim to promote harmony between human habitation and the natural world with prime examples being Robie House and Fallingwater.
What was Wright's intention regarding humans and nature?
to promote harmony

Some of the best examples of later Islamic mosaics were produced in Moorish Spain. The golden mosaics in the mihrab and the central dome of the Great Mosque in Corduba have a decidedly Byzantine character. They were made between 965 and 970 by local craftsmen, supervised by a master mosaicist from Constantinople, who was sent by the Byzantine Emperor to the Umayyad Caliph of Spain. The decoration is composed of colorful floral arabesques and wide bands of Arab calligraphy. The mosaics were purported to evoke the glamour of the Great Mosque in Damascus, which was lost for the Umayyad family.
Where are some of the best examples of islamic mosaic work found?
Moorish Spain