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## Homework Statement

Let X = {1,2,3,4} and let G = (V,E) be the graph whose vertices are the 2-element and 3-element subsets of X and where A is adjacent to B if |A and B| = 2. That is:

[tex]

V = nCr(X,2) or nCr(X,3)

E = {{A,B}:A,B\inV and |A\capB|=2}

[/tex]

(a) Draw the diagram of the graph G

(b) Use Theorem (*) to show that G is Eulerian.

(c) Exhibit an Euler circuit

## Homework Equations

(*) Let G be a connected general graph. Then G has a closed Eulerian trail if and only if the degree of each vertex is even.

## The Attempt at a Solution

Well the 2-element subsets of X are {1,2},{1,3},{1,4},{2,3},{2,4},{3,4}.

and the 3-element subsets of X are {1,2,3},{1,3,4},{1,2,4},{2,3,4}.

How can these be vertices? And would this be more than one graph? I am confused by this.