# Thread: Simple graph theory, but can't figure out what they're looking for

1. ## Simple graph theory, but can't figure out what they're looking for

Let A and B be 2 Eulerian graphs with no common vertices. Let v1 be a vertex of A and v2 be a vertex of B. Let G be the graph that is formed by taking AUB and adding the edge v1v2. What can be said about G?

Is it simply that G is Eulerian since we are just adding one more edge and we are not changing the number of vertices, or is there something else that can be said?

2. Originally Posted by zhupolongjoe
Let A and B be 2 Eulerian graphs with no common vertices. Let v1 be a vertex of A and v2 be a vertex of B. Let G be the graph that is formed by taking AUB and adding the edge v1v2. What can be said about G?
It seems that I have given this warning several times today: There are no standard notations.
Usually we say that a graph is Eulerian if it has an Eulerian circuit (all vertices of even degree).
But there are texts that use the term if a graph is simply traceable.

If you have two disjoint graphs of all even vertices then by connecting them with one edge, you have introduced two odd vertices. Therefore the new graph is not Eulerian but it is traceable.

3. Thanks. I see the distinction there that is used. My book uses the Eulerian circuit vs. Eulerian trail.