reserve G for Graph,
  k, m, n for Nat;

theorem Th2:
  for G being Graph holds rng (the Source of G) \/ rng (the Target
  of G) c= the carrier of G
proof
  let G be Graph;
  rng (the Source of G) c= the carrier of G & rng (the Target of G) c= the
  carrier of G by RELAT_1:def 19;
  hence thesis by XBOOLE_1:8;
end;
