Euler posed the problem: Could he find a walk through the city that crossed each bridge only once? To find a provable answer, he needed a suitable generalization for analysis. Recognizing that the important aspects were the land mass, the bridges connecting them, and the sequence in which the bridges were crossed, he eliminated superfluous features. He abstracted each land mass into a node and each bridge that connected these nodes as an edge. With this generalization, he proved that there was no way to reach all regions without crossing a bridge more than once.