In mathematical logic and computer science, the Kleene star (or Kleene operator or Kleene closure) is a unary operation, either on sets of strings or on sets of symbols or characters.

Jonathan Klein Photos that changed the world

Naomi Klein Addicted to risk

In 1935, Levin published information about several more cases, including one described by Kleine.

According to estimates by Robert Klein of Georgia State University, homeowners insurance premiums in Louisiana had already gone up by 70 between 1997 and 2005.

It is widely used for regular expressions, which is the context in which it was introduced by Stephen Kleene to characterise certain automata, where it means zero or more .

An article by Ernst Fehr at the University of Zurich and Alexander Klein and Klaus Schmidt at the University of Munich in the January 2007 issue of the journal Econometrica shows how people design economic relationships based on their knowledge of the circumstances in which people are trustworthy.

Photographs do more than document history they make it. At TED University, Jonathan Klein of Getty Images shows some of the most iconic, and talks about what happens when a generation sees an image so powerful it can't look away or back.