Russell's paradox is a problem Bertrand Russell published in 1901 about the foundations of mathematics. Consider the set of all sets that are not members of themselves. If that set is not a member of itself, it must be, yet if it is, it cannot be. The contradiction shows that a set theory allowing unrestricted definitions of sets must fail. Russell also showed the problem affected the system built by Gottlob Frege, which undermined Frege's attempt to reduce mathematics to logic. Zermelo and others then proposed revised axioms in 1908 to avoid it.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.