reserve GS for GraphStruct;
reserve G,G1,G2,G3 for _Graph;
reserve e,x,x1,x2,y,y1,y2,E,V,X,Y for set;
reserve n,n1,n2 for Nat;
reserve v,v1,v2 for Vertex of G;

theorem
  for G being _Graph, G1,G2 being Subgraph of G st G1 c< G2 holds (ex v
  being object st v in the_Vertices_of G2 & not v in the_Vertices_of G1) or
   ex e being object st e in the_Edges_of G2 & not e in the_Edges_of G1
proof
  let G be _Graph, G1,G2 be Subgraph of G;
  assume G1 c< G2;
  then the_Vertices_of G1 c< the_Vertices_of G2 or the_Edges_of G1 c<
  the_Edges_of G2 by Th98;
  hence thesis by XBOOLE_0:6;
end;
