In the third verse, Lao-tzu uses Wu and Yu as the basis to describe the true relationship between the myriad things as Heng Wu and Heng Yu. We may call them the true manifestations of Tao in the myriad things.
To be true, these manifestations must cover the whole domain of Tao. Wu and Yu are two opposite sub-domains of the whole, so these objects must be re-integrated into a whole to represent the realities of Tao.
Lao-tzu shows the results of such subtle re-integrations in Verse 3. In the integration, Wu and Yu become intermixed.
- In Heng Wu, Lao-tzu uses the word “subtlety 妙” to indicate “subtle appearances of the myriad things.” Such subtle appearance (Yu) appears with and thus complements Wu to form Heng Wu.
- In Heng Yu, Lao-tzu uses the word “borderless 徼” to indicate “disappearance of the boundaries between the myriad things.” Such disappearance of the boundaries (Wu) appears with and thus complements Yu to form Heng Yu.
In Lao-tzu’s description, Wu and Yu are complimentary in the formation of Heng Wu and Heng Yu. Therefore, each manifestation is a complementarity of Wu and Yu.
Here we can see how Lao-tzu uses complementarity, superposition, or entanglement [See definitions in the Appendix] of Wu and Yu to describe the manifestations of Tao. Some Yu must appear together within Wu in forming Heng Wu and some Wu must appear together within Yu in forming Heng Yu. Thus, Heng Wu and Heng Yu have overcome the fragmentation of Tao into Wu and Yu, and preserved the wholeness necessary to represent Tao. We shall consider Heng Wu and Heng Yu to be wholes and non-dualistic.
This verse shows that we can use “superimposed” objects to describe the true manifestations. Both objects must appear simultaneously and complementarily in each true manifestation. Each true manifestation can cover the whole domain.
A few comments on the terms “manifestation” and “principle” may be useful here. We may take manifestations to be (1) the “revelations of Tao” or (2) our observations of nature. In either way, each manifestation should reveal the principle of Tao. There may be many manifestations, but there is only one principle. All manifestations will show the same principle. This is the mystery of Tao.
 Description of nature in classical physics is either “particles” or “waves.” In quantum theory, “particle” and “wave” become complementary. In relativity, space and time become complementary.