reserve a,b,c,d for Real;
reserve z,z1,z2 for Complex;

theorem Th4:
  Re 0 = 0 & Im 0 = 0
proof
  reconsider zz=0 as Element of REAL by XREAL_0:def 1;
  0 = [*zz,zz*] by ARYTM_0:def 5;
  hence thesis by Lm2;
end;
