Continuing the architectural theme, Isabel at God Plays Dice has a post on the ultimate fate of the real world KÃ¶nigsberg bridge problem. KÃ¶nigsberg had seven bridges, and in 1736 Euler proved it was impossible to find a path that allowed you to cross each bridge exactly once.

In World War II, several of the bridges were bombed, and later some were replaced. In present-day KÃ¶nigsberg, now Kaliningrad, there are now only five bridges, and you can now find a path that allows you to cross each bridge exactly once.