 Birrell suggests this abstract Yin-Yang dualism between the two primeval spirits or gods may be the "vestige of a much older mythological paradigm that was then rationalized and diminished", comparable to the Akkadian "Enûma Eliš" creation myth of Abzu and Tiamat, male fresh water and female salt water.The "Lingxian" (), written around 120 by the polymath Zhang Heng, thoroughly accounts for the creation of Heaven and Earth.Before the Great Plainness [or Great Basis, Taisu, ] came to be, there was dark limpidity and mysterious quiescence, dim and dark.