For those that won't click through, a very short explanation given by the author: "Is Planet Nine gravitationally dominant? I think it is safe to say that any p

For those that won't click through, a very short explanation given by the author: "Is Planet Nine gravitationally dominant? I think it is safe to say that any planet whose existence is inferred by its gravitational effects on a huge area of the solar system is gravitationally dominant." He then goes on to give a more technical argument.