
theorem Th2:
  for x1 be Element of F_Complex for x2 be Complex st x1 =
  x2 holds - x1 = - x2
proof
  let x1 be Element of F_Complex;
  let x2 be Complex;
  assume
A1: x1 = x2;
  reconsider x2 as Element of COMPLEX by XCMPLX_0:def 2;
  -x2 in COMPLEX by XCMPLX_0:def 2;
  then reconsider x9=-x2 as Element of F_Complex by Def1;
  x1 + x9 = 0.F_Complex by A1,Def1;
  hence thesis by RLVECT_1:def 10;
end;
