
theorem Th21:
  for n being non zero Element of NAT, x being Element of
  F_Complex holds x in n-roots_of_1 iff x is CRoot of n,1_F_Complex
proof
  let n be non zero Element of NAT, x be Element of F_Complex;
  hereby
    assume x in n-roots_of_1;
    then ex y being Element of F_Complex st y=x & y is CRoot of n, 1_F_Complex;
    hence x is CRoot of n,1_F_Complex;
  end;
  thus thesis;
end;
