[T]he Threefold Track and the One Buddha-vehicle are two names of the same thing: the one is in the three, and the three are in the one. Chih-i illustrates this indefinite nature by quoting the formula of affirmation, negation and double negation (i.e., one, not one, neither one nor not one). (i) The formula of affirmation “one” expresses the concept “Supreme Truth” (Ti-i-i Ti) so that the absoluteness of the True Reality is denoted. Chih-i uses this term Supreme Truth to declare that all dharmas are converged into One Buddha-vehicle. (ii) The formula of negation “not one” expresses the concept tathāgatagarbha (Ju-lai-tsang), indicating the functional nature of the True Reality. This term is used by Chih-i to refer to the richness of the tathāgatagarbha in terms of its immeasurable dharma-doors for teaching sentient beings. To suite the different faculties of beings, the Buddha expounds upon various vehicles in his teaching. (iii) The formula of double negation “neither one nor not one” delineates the concept “Supreme Meaning of Emptiness” (Ti-i-i K’ung). This term refers to the function that rises from the nature of emptiness, and Chih-i associates it with the skillful and expedient means of True Reality: The Relative contains the Ultimate, and vice versa. The Buddha teaches the dharma according to these conditions. The teaching seems to be definite but not definite, since the Buddha expounds the Ultimate of the One Buddha-vehicle as well as the Relative of the Three Vehicles (śrāvaka, pratyekabuddha, and bodhisattva). Although there is Relative of the Three Vehicles in the teaching of the Buddha, in the end, all of them are converged into the Ultimate of the One Vehicle. (Vol. 2, Page 241)