reserve z,z1,z2,z3,z4 for Element of F_Complex;

theorem
  z2 <> 0.F_Complex implies z1 / z2" = z1 * z2
proof
  reconsider z19=z1,z29=z2 as Element of COMPLEX by Def1;
  assume z2 <> 0.F_Complex;
  then z2" <> 0.F_Complex & z2" = z29" by Th5,VECTSP_1:25;
  hence z1 / z2" = z19 / z29" by Th6
    .= z1 * z2 by XCMPLX_1:219;
end;
