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).
A U.S. Air Force CV-22 Osprey from the 8th Special Operations Squadron, Air Force Special Operations Command, Hurlburt Field, Fla., flies a night mission in support of Operation Enduring Freedom, Afghanistan on April 28, 2010.(U.S. Army photo)(Released).lthough some Taliban and al-Qaeda members managed to escape into Pakistan, the coalition air campaign essentially ended on December 18, 2001. In just 102 days after the September 11 attacks, the Taliban regime had been overthrown and the al-Qaeda leadership dispersed.