
theorem Th10:
  for X being non empty set, x1, x2 being Element of X st UnitBag
  x1 = UnitBag x2 holds x1 = x2
proof
  let X be non empty set, x1, x2 be Element of X such that
A1: UnitBag x1 = UnitBag x2 and
A2: x1 <> x2;
  1 = (UnitBag x2).x1 by A1,Th9
    .= 0 by A2,Th9;
  hence contradiction;
end;
