You can: the equation x^2 = x holds for 1, but not for -1, so you can separate them. There is no way to write an equation without mentioning i (excluding cheati

You can: the equation x^2 = x holds for 1, but not for -1, so you can separate them. There is no way to write an equation without mentioning i (excluding cheating with Im, which again can't be defined without knowing i) that holds for i, but not -i.