- 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.
- A Portrait of Tenochtitlan (thomaskole.nl)
The year is 1518. Mexico-Tenochtitlan, once an unassuming settlement in the middle of Lake Texcoco, now a bustling metropolis. It is the capital of an empire ruling over, and receiving tribute from, more than 5 million people. Tenochtitlan is home to 200.000 farmers, artisans, merchants, soldiers, priests and aristocrats. At this time, it is one of the largest cities in the world.