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

theorem
  z / (1.F_Complex) = z
proof
  reconsider z1=z as Element of COMPLEX by Def1;
  1.F_Complex = 1r by Def1;
  hence z / (1.F_Complex) = z1 / 1r by Th6
    .= z;
end;
