Usage Click on an edge or a vertex. Double click on a (\(-1\))-vertex.
Note. The red edge corresponds to the point which is not allowed to be blowed up in the configuration of negative curves.
The red vertex corresponds to the (-1)-curve which does not have any non-intersection point that is allowed to be blowed up in the configuration of negative curves.
The vertex corresponding to the red (-1)-curve which has a point with multiplicity at least 2 in the configuration of negative curves is not drawn in the dual graph.