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A matchstick graph is a set of unit-length sticks in the plane, with the proviso that two sticks may meet only at their endpoints. The points that are matchstick-ends are called the vertices of the graph. For example, an equilateral triangle with unit side-length is a matchstick graph with 3 vertices in which each vertex is connected to two others.

Find a matchstick graph in which each vertex is connected to exactly three other vertices. Try to minimize the number of vertices.© Copyright 1996 Stan Wagon. Reproduced with permission.

2 October 1998