Then the whole chain of dependent beings is dependent on nothing and could not exist if there is no independent being.
Much more abstract philosophical language, the proof goes because of this. Every being that exists either exists on it’s own, by its very own essence or nature, or it will not occur on it’s own. Then it exists necessarily and eternally, and explains itself if it exists by its own essence. It cannot not occur, as being a triangle cannot n’t have three edges. If, having said that, a being exists however by a unique essence, then it requires a cause, grounds outside it self because of its presence.