eulerian是指每一條線路都只走一次。這是1736年Leonhard Euler while由在解決"七座橋"問題時發明的
In the mathematical field of graph theory, an Eulerian path is a path in a graph which visits each edge exactly once. They were first discussed by Leonhard Euler while solving the famous Seven Bridges of Königsberg problem in 1736. Mathematically the problem can be stated like this.