GrisonsThe Grisons (ɡriːˈzɒ̃, ɡʁizɔ̃) or Graubünden (ɡraʊˈbʏndn̩), more formally the Canton of the Grisons or the Canton of Graubünden, is one of the twenty-six cantons of Switzerland. It has eleven districts, and its capital is Chur. The German name of the canton, Graubünden, translates as the "Grey Leagues", referring to the canton's origin in three local alliances, the Three Leagues. The other native names also refer to the Grey League: Grischùn in Sutsilvan, Grischun in the other forms of Romansh, and Grigioni in Italian.
Unconventional (oil & gas) reservoirUnconventional (oil & gas) reservoirs, or unconventional resources (resource plays) are accumulations where oil & gas phases are tightly bound to the rock fabric by strong capillary forces, requiring specialised measures for evaluation and extraction. Petroleum reservoir Oil and gas are generated naturally at depths of around 4 or 5 kms below Earth’s surface. Being lighter than the water, which saturates rocks below the water table, the oil and gas percolate up through aquifer pathways towards Earth's surface (through time) by buoyancy.
Empty setIn 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. Any set other than the empty set is called non-empty. In some textbooks and popularizations, the empty set is referred to as the "null set".
