
theorem Th16:
  for V being RealUnitarySpace, W being Subspace of V, v being
  VECTOR of V st v in W holds - v in W
proof
  let V be RealUnitarySpace;
  let W be Subspace of V;
  let v be VECTOR of V;
  assume v in W;
  then (- 1) * v in W by Th15;
  hence thesis by RLVECT_1:16;
end;
