The Swiss mathematician Euler is universally credited with having
produced the first paper on graph theory. By examining the node-vertex
relationships in a graph representing the seven bridges, two islands, and
two banks of the Prengel River, he solved the “Koenigsberg Bridge Puzzle”
which posed the problem of whether it is possible to begin at any of the
four land areas, walk across each bridge exactly once, and return to the
starting point.