Seven Bridges of Königsberg
Ehler forged a friendship with fellow Prussian mathematician Heinrich Kuhn. This friendship would then blossom into a correspondence with another mathematician, Leonhard Euler. The correspondence initially began in March 1735 with a letter sent by Ehler to Euler. The correspondence itself is lost, but we can find the main thread of their relationship with Euler's first letter of response. In the letter, Euler talks of the problem of the Seven Bridges of Königsberg, a problem that Ehler brought to Euler's attention. The reason for such an inquiry was the desire by Kuhn and Ehler to encourage mathematical advancements within Prussia. The letter itself reads: