Lightness, heaviness and gravity Original Research Article

The gravity image of a graph H in the family of graphs image is the greatest integer n with the property that for every integer m, there exists a supergraph image of H such that each subgraph of G, which is isomorphic to H, contains at least n vertices of degree image in G. We study the basic properties of the gravity function for various families of plane graphs. We also introduce and study the almost-light graphs and the absolutely heavy graphs. The paper concludes with few open problems.