
theorem Th8:
  for A being set, b being Rbag of A st b = EmptyBag A holds Sum b = 0
proof
  let A be set, b be Rbag of A;
  set cS = canFS(support b);
  assume b = EmptyBag A;
  then b*cS = <*>NAT;
  hence thesis by Def2,RVSUM_1:72;
end;
