reserve G for _Graph;
reserve G2 for _Graph, G1 for Supergraph of G2;
reserve V for set;
reserve v for object;

theorem Th98:
  for G2, v for G1 being addVertex of G2, v holds v is Vertex of G1
proof
  let G2, v;
  let G1 be addVertex of G2, v;
  v in {v} by TARSKI:def 1;
  hence thesis by Th90;
end;
