reserve G for _Graph;

theorem Th49:
  for G1, G2 being _Graph st G1 == G2
  holds VertexAdjSymRel(G1) = VertexAdjSymRel(G2)
proof
  let G1, G2 be _Graph such that A1: G1 == G2;
  thus VertexAdjSymRel(G1)
     = VertexDomRel(G2) \/ ((VertexDomRel(G1))~) by A1, Th19
    .= VertexAdjSymRel(G2) by A1, Th19;
end;
