Double Bar. The double bar symbol is used to denote certain kinds of norms in mathematics (e.g., or). It is also used to denote parallel lines, as in, and in an older notation for the covariant derivative. In this work, the notation or is reserved for matrix and function norms, respectively.
The F-4 Phantom II remained in use by the U.S. in the reconnaissance and Wild Weasel (Suppression of Enemy Air Defenses) roles in the 1991 Gulf War, finally leaving service in 1996. It was also the only aircraft used by both U.S. flight demonstration teams: the USAF Thunderbirds (F-4E) and the US Navy Blue Angels (F-4J).
The war is also known under other names, such as the Persian Gulf War, First Gulf War, Gulf War I, Kuwait War, First Iraq War, or Iraq War before the term Iraq War became identified instead with the 2003 Iraq War (also referred to in the U.S. as  Operation Iraqi Freedom ).he war has also earned the nickname Video Game War after the daily broadcast of images from cameras on board U.S. bombers during Operation Desert Storm. The initial conflict to expel Iraqi troops from Kuwait began with an aerial and naval bombardment on 17 January 1991, continuing for five weeks.