The system of the monad, constructed through the tetraktys of the decad, which serves as an underlying philosophy in Sethian Gnosticism. It is developed from the creation myths. The system is like, and based upon that of Pythagoreans, and resembles the principles of the ancient Chinese philosophy of the Tai Chi., which is based upon the ogdoad. The system is based upon working variations of numerical values. Turner states, "....vigorous arithmological speculation on the first ten numbers, but especially the first four numbers, comprising the Pythagorean tetraktys (the {mode} of the first four numbers). This was carried on by such Pythagoreanizing Platonists as Theon of Smyrna and Nicomachus of Gerasa, who in turn depend in part on similar arithmological and mathematical theories produced by such early first century Platonist figures as Dercyllides, Adrastos of Aphrodisias (a Peripatetic commentator on Plato's Timaeus) and Thrasyllos, a court philosopher under the Emperor Tiberius. The harmonic ratios produced by these first four numbers and the geometric entities of point, line, surface, and solid had been applied to the structure and the creation of the world soul long before by Plato and his successors in the Old Academy, especially Speusippus and Xenocrates. (See Turner, See also; "The History of Chinese Philosophy, Vol. 2"., by Fung Yu-Lan, Princeton, 1953, See also; "A Valentinian Exposition".)