American teacher who is known as a mathematician working in analysis and combinatorics and has worked as a professor of Mathematics at Pennsylvania State University.
He earned a PhD from the University of Pennsylvania in 1964.
He became a member of the National Academy of Sciences and was president of the American Mathematical Society from 2008 until 2009.
He was born into an American family in Salem, Oregon.
Another teacher who earned a PhD from the University of Pennsylvania like him is Noam Chomsky.