/// <summary>
/// (internal) - constructor for starting to configure a tetrahedral centre.
/// </summary>
/// <param name="gb">the graph builder </param>(where we came from)
/// <param name="u"> the vertex to</param>
internal ExtendedTetrahedralBuilder(GraphBuilder gb,
int u)
{
this.gb = gb;
this.u = u;
}
public GeometricBuilder(GraphBuilder gb, int u, int v)
{
this.gb = gb;
this.u = u;
this.v = v;
}