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 Gulf War (2 August 1990 â 28 February 1991), codenamed Operation Desert Shield (2 August 1990 â 17 January 1991) for operations leading to the buildup of troops and defense of Saudi Arabia and Operation Desert Storm (17 January 1991 â 28 February 1991) in its combat phase, was a war waged by coalition forces from 35 nations led by the United ...