has been a vigorous discussion in Chinese philosophy regarding the ultimate origin of Zhou Dunyi's diagram. Zhu Xi (12th century) insists that Zhou Dunyi had composed the diagram himself, against the prevailing view that he had received it from Daoist sources. Zhu Xi could not accept a Daoist origin of the design, because it would have undermined the claim of uniqueness attached to the Neo-Confucian concept of dao. Ming and Qing eras While Zhou Dunyi (1017–1073) popularized the circular diagram, the introduction of "swirling" patterns first appears in the Ming period. Zhao Huiqian (趙撝謙, 1351–1395) was the first to introduce the "swirling" variant of the taijitu in his Liushu benyi (六書本義, 1370s). The diagram is combined with the eight trigrams (bagua) and called the "River Chart spontaneously generated by Heaven and Earth". By the end of the Ming period, this diagram had become a widespread representation of Chinese cosmology. The dots were introduced in the later Ming period (replacing the droplet-shapes used earlier, in the 16th century) and are encountered more frequently in the Qing period. The dots represent the seed of yin within yang and the seed of yang within yin; the idea that neither can exist without the other. Lai Zhide's design is similar to the gakyil (dga' 'khyil or "wheel of joy") symbols of Tibetan Buddhism; but while the Tibetan designs have three or four swirls (representing the Three Jewels or the Four Noble Truths, i.e. as a triskele and a tetraskelion design), Lai Zhide's taijitu has two swirls, terminating in a central circle. Modern yin-yang symbol The Ming-era design of the taijitu of two interlocking spirals was a common yin-yang symbol in the first half of the 20th century. The flag of South Korea, originally introduced as the flag of Joseon era Korea in 1882, shows this symbol in red and blue. This was a modernisation of the older (early 19th century) form of the Bat Quai Do used as the Joseon royal standard. Since the 1960s, the He tu symbol, which combines the two interlocking spirals with two dots, has more commonly been used as a yin-yang symbol. compare with In the standard form of the contemporary symbol, one draws on the diameter of a circle two non-overlapping circles each of which has a diameter equal to the radius of the outer circle. One keeps the line that forms an "S", and one erases or