Chu-san Hsien-i (Abiding in the three and revealing the one) is the function related to the Subtlety of Response. Chih-i says that this is spoken of in terms of the relative knowledge of the Buddha, which is applied expediently by the Buddha to transform living beings. The expedient means used (e.g. abiding in the three vehicles) is for the sake of aiding the manifestation of the Supreme Truth (i.e., revealing the one). (Vol. 2, Page 445)