(First of Forty Tenets of Plum Village)
"Space is not an unconditioned dharma. It manifests together with time, matter and consciousness."
(Second of Forty Tenets of Plum Village)
"In the historical dimension, every dharma is a conditioned dharma. In the ultimate dimension, every dharma is an unconditioned dharma."
So, in the Heart Sutra, two types of the ultimate truth are described. One is the ultimate truth in the phenomenal world which is "interdependent co-arising". The other is the ultimate truth in the noumenal world which is "non-separation or wholeness".
1) The ultimate truth in the phenomenal world (historical dimension)
"Interdependent co-arising" is the skillful means to transcend the duality in the phenomenal world, or the historical dimension. It is also called "Emptiness", "Interbeing" in other words. In the phenomenal world, there is only the relative truth. So, there are pairs of opposites such as birth and death, right and left. The method to transcend the duality in order to attain the non-duality here is the two sides of the same coin. If we understand that A and B are two sides of the same coin, we can transcend the duality and attain the non-duality. This method may be a little tricky because A and B are not two but are not also one. But it can't be helped because all phenomena are based on the duality in the phenomenal world, or the historical dimension. "Interdependent co-arising" must be the only way to transcend the duality in the phenomenal world.
In the Heart Sutra, the ultimate truth in the phenomenal world (historical dimension) is described from the beginning of "観自在菩薩 (Avalokiteshvara)" till "不増不減 (no increasing and no decreasing)". And its logic is the following.
"A is made of non-A elements.
So, A is not A.
A is everything except for A.
So, A is no other than B.
Namely, A is B."
A can be liken to suffering and B can be liken to happiness.
"Suffering is made of non-suffering elements.
So, suffering is not suffering.
Suffering is everything except for suffering.
So, suffering is no other than happiness.
Namely, suffering is happiness."
Now you can understand the meaning of "Suffering is no other than happiness." Suffering and happiness are two sides of the same coin. So, if there is suffering, happiness must be there at the same time. All we need is to observe from different angle. Actually, when we suffer, we can find out happiness at the same time if we observe from different angle.
That's why "Interdependent co-arising" enables us to transcend separations, discrimination, or the duality. We can stop separating ourselves from others through this non-duality. So, there is no space for any afflictions to arise. Therefore, we can liberate ourselves from sufferings.
This formula is clearly mentioned in the Heart Sutra as follows:
色不異空: Form is no other than emptiness.
<That's because form is made of non-form elements, namely emptiness.>
空不異色: Emptiness is no other than form.
<That's because emptiness is made of non-emptiness elements, namely form.>
色即是空: Form is namely emptiness (empty of separate existence = non-form elements).
空即是色: Emptiness (empty of separate existence = non-form elements) is namely form.
In other words, A is made of non-A elements. So, A is no other than non-A. Namely, A is non-A.
Meanwhile, non-A is made of non-non-A elements. So, non-A is no other than non-non-A. Namely, non-A is A.
David Bohm explained more simply; "Everything is internally related to everything. Everything contains everything." The Buddha and David Bohm said the same thing. In this sense, Buddhism and quantum physics are very similar. All phenomena are conditioned because there are only relative truths in this phenomenal world, as Albert Einstein scientifically proved it by the general theory of relativity.