- Samurai (侍) were the hereditary military nobility and officer caste of medieval and early-modern Japan from the late 12th century until their abolition in the 1870s during the Meiji era. They were the well-paid retainers of the daimyo, the great feudal landholders. They had high prestige and special privileges.
- Empty set (Wikipedia)
In mathematics, the empty set is the unique set having no elements; its size or cardinality (count of elements in a set) is zero. Some axiomatic set theories ensure that the empty set exists by including an axiom of empty set, while in other theories, its existence can be deduced. Many possible properties of sets are vacuously true for the empty set.
