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

theorem
  z <> 0.F_Complex implies z / z = 1.F_Complex
proof
  reconsider z1=z as Element of COMPLEX by Def1;
  assume
A1: z <> 0.F_Complex;
  hence z / z = z1 / z1 by Th6
    .= 1r by A1,Th7,XCMPLX_1:60
    .= 1.F_Complex by Def1;
end;
