
theorem
  for I being non degenerated domRing-like commutative Ring for u being
  Element of the_Field_of_Quotients(I) holds -u = (quotaddinv(I)).(u)
proof
  let I be non degenerated domRing-like commutative Ring;
  let u be Element of the_Field_of_Quotients(I);
  reconsider z = (quotaddinv(I)).u as Element of the_Field_of_Quotients(I) by
Th32;
  z + u = 0.the_Field_of_Quotients(I) by Th28;
  hence thesis by RLVECT_1:6;
end;
