In October 2015 my time training mathematics teachers at a French high school in Port Vila, Vanuatu, was coming to an end. The principal invited me to share kava, a traditional drink in the country.

Proceedings of the National Academy of Sciences of the United States of America PNAS is the world's most-cited multidisciplinary scientific serial. It publishes high-impact research reports, ...

During the 18th century the denizens of the Prussian city of Königsberg wrestled with a puzzle: How could they find a walking path through the city that crossed each of its storied seven bridges ...