In 1736 the Swiss math­e­mati­cian Leon­hard Euler ended a debate among the cit­i­zens of Konigs­berg, Prussia, by drawing a graph. The Pregel River divided the city, now Kalin­ingrad, Russia, into four sec­tions. Seven bridges con­nected them. Could a person cross all seven without walking over the same one twice?

Read the article at Popsci →