Madhyamaka in Zen Buddhism

Now, the fount of the One Mind is free from existence and non-existence and is independently pure. The ocean of the three levels of apprehension of emptiness2 merges the absolute and conventional and is perfectly calm. While calmly fusing two, it is not one. Independently pure, it is free from extremes, but does not lie in the center. Not lying in the center, yet free from extremes, non-existent dharmas do not abide in non-existence, and marks that are not non-existent do not abide in existence.

Since it is not one yet merges dualities, non-absolute phenomena are not originally conventional, and the non-conventional principle is not originally absolute. Since it merges dualities and yet is not one, there is nothing thatthe natures of the absolute and conventional do not establish, and there are no marks of purity and pollution not contained within. Since it is free from extremes, yet not in the center, there are no existent or non-existent dharmas that are not created, and no positive or negative implications that are not subsumed.

Accordingly, without refutation, there is nothing not refuted; without positing, there is nothing not posited. We can call it the ultimate principle of no-principle, the great being-so of not being-so. This is the general message of this sūtra. It is precisely because it is the great being-so of not being-so that the words of the speaker mysteriously match the center of the ring.3 Since it is the ultimate principle of no principle, the doctrine that is explained transcends this world. Since it leaves nothing unrefuted, it is called the Vajrasamādhi. Since there is nothing it does not establish, it is called the Sūtra of the Compendium of the Great Vehicle. None of its meanings and doctrines fall outside of these two. Therefore it is also called the Numberless Meanings and Doctrines. But being constrained to tender only one title, we call it the Vajrasamādhi-sūtra.

-Preface to the Exposition to the Vajra Samadhi Sutra, a commentary by Zen Master Won-Hyo

The above commentary by the Zen Master should open the eyes of the Tibetan scholars from the various lineages such as Sakya, Gelug, Kagyu and Nyingma. I'd like to think of it as the Madhyamaka in Zen. But Won Hyo is talking about the nature of the One Mind. He is not refuting someone else's theory to prove he has the most correct emptiness theory.