"Closure" is a property which a set either has or lacks with respect to a given operation. A set is closed with respect to that operation if the operation can always be completed with elements in the set. For example, the set of even natural numbers,...

In mathematics, a set is said to be closed under some operation if the operation on members of the set produces a member of the set. For example, the real numbers are closed under subtraction, but the natural numbers are not: 3 and 7 are both natural...

Historic Tempelhof Airport — which played a key role in the Berlin airlift in the wake of World War II — will close to passengers in 2008, Germany's top administrative court confirmed Tuesday.The court threw out a bid to prevent Tempelhof's closure as part of...

Closing U.S. borders would be the last option in combating the spread of bird flu, a senior State Department official said Monday. It would not be likely to decrease the number of cases, would interrupt essential services and would disrupt...

Authorities briefly reopened two highways crossing north Florida into Georgia on Sunday before dense wildfire smoke forced them to again halt traffic, while hundreds of Florida residents waited to return to their threatened homes.Officials said Sunday that the wildfire that had raced through the Okefenokee...

About 2,000 people protested at the border terminal between Egypt and the Gaza Strip on Thursday, demanding the crossing be opened to allow thousands of Palestinians trapped in Egypt to return.The Rafah border terminal, the only gateway for Palestinian travelers to the world, has been...