In mathematical set theory and model theory, a stationary set is one that is not too small in the sense that it intersects all club sets, and is analogous to a set of non-zero measure in set theory. There are at least three closely related notions of stationary set, depending on whether one is looking at subsets of an ordinal, or subsets of something of given cardinality, or a powerset. Stationery is a mass noun referring to commercially manufactured writing materials, including cut paper, envelopes, writing implements, continuous form paper, and other office supplies. Stationery includes materials to be written on by hand (e.g., letter paper) or by equipment such as computer printers.