In the second chapter of The Infinite Meanings Sutra, we get this discussion of emptiness:

The Buddha replied: “O you of good intent! This particular Dharma approach is known as Infinite Meanings. A bodhisattva who wishes to achieve mastery in the practice of Infinite Meanings must perceive and observe that, in and of themselves, all phenomena intrinsically have been, successively will be, and currently are tranquil and empty in nature and aspect, without greatness or smallness, without origination or cessation, neither fixed nor moving, non-advancing and non-retreating. Like the emptiness of space, they are without duality. Living beings, however, thoughtlessly and falsely make polar assessments: ‘It is this,’ ‘It is that’; ‘It is gain,’ ‘It is loss.’ Unwholesome thoughts arise in them, producing harmful karmic causes. They cycle and recycle in the six realms of existence, piling up harmful passions and sufferings, and for hundreds of millions of myriads of kalpas they cannot break themselves free. Clearly perceiving this, the great-being bodhisattva must bring forth a mind of mercy and give rise to great compassion—particularly wishing to relieve living beings of suffering.

“He or she must then more completely fathom all phenomena: aspects of phenomena being as such, as such will phenomena come forth; aspects of phenomena being as such, as such will phenomena settle; aspects of phenomena being as such, as such will phenomena change; aspects of phenomena being as such, as such will phenomena become void. Aspects of phenomena being as such, an unwholesome phenomenon is able to come forth. Aspects of phenomena being as such, a wholesome phenomenon is able to come forth. So it is also with regard to settling, changing, and becoming void.

“After perceiving, observing, and fully understanding everything about these four modes from beginning to end, the bodhisattva must next perceive and observe that all phenomena are impermanent—coming forth and becoming void over and over again from moment to moment, and further grasp that their coming forth, settling, changing, and becoming void are instantaneously occurring. Having perceived and comprehended this, the bodhisattva will then have insight into the various conditioned desires of the senses of living beings.

When I read this it struck me how this is the foundation upon which Ichinen Sanzen is built.