Hokke Sanbu-kyo (Threefold Lotus) Sutra (法華三部経)
The "Hokke Sanbu-kyo (Threefold Lotus Sutra)" is a set of sutras of Mahayana Buddhism. It is referred as ten volumes of the Lotus Sutra, or The Lotus Sutra and Its Opening and Closing Sutras.
Furthermore, threefold refers here to the three sutras: "Muryo gikyo" (Sutra of Immeasurable Meanings), "Myoho-renge-kyo" (the Lotus Sutra) and, "Bussetsu Kanfugen bosatsu Gyoho-kyo" (Sutra of Meditation on the Bodhisattva Universal Virtue).
Summary
It is said that the theory of regarding the three sutras as a single sutra was originated in the ideas of Chigi. The details are as follows.
"Myoho-renge-kyo" (the Lotus Sutra) translated into Chinese by Kumarajiva is not complete by itself: it was constitutively translated as the main part of 'Lotus Sutra, the supreme teaching which Shakyamuni ultimately revealed.'
"Hokke Sanbu-kyo" translated by Kumarajiva is composed of the three following parts; one volume of "Muryo gikyo" (Sutra of Immeasurable Meanings) as the opening part of the sutra, twenty-eight chapters in eight volumes of "Myoho-renge-kyo" (the Lotus Sutra) as the main sutra, and one volume of "Bussetsu Kanfugen bosatsu Gyoho-kyo" (Sutra of Meditation on the Bodhisattva Universal Virtue) as the closing part.
Japan's Tendai Sect (Sanmon school and Jimon school) and various schools of Hokke sect, such as Nichiren Sect or Nichiren Shoshu school, regard the theory as their doctrine and the three sutras as the basis.