Ichinen sanzen is a complex and challenging concept, and in his doctrinal instruction, Nichiren frequently concentrated on one of its key component principles: the mutual inclusion of the ten dharma realms (jikkai gogu). Traditional Buddhist cosmology divides saṃsāra or the realm of rebirth for unenlightened beings into a hierarchy of six paths: hell dwellers, hungry ghosts (preta), animals, demigods (asura), humans, and gods (deva). Above these, Tendai doctrine places four more realms characterized by ascending levels of awakening: the two realms of the śrāvakas and pratyekabuddhas, who cultivate the aims of detachment and cessation of desire set forth in the so-called Hinayāna teachings, aiming for the goal of Nirvāṇa; bodhisattvas, who strive for the liberation of all beings; and fully realized buddhas. In contrast to the buddha realm, which represents enlightenment, the other nine realms represent various levels of delusion, or states not yet fully awakened. Being empty of fixed, independent existence, all ten interpenetrate, meaning that each realm contains all ten within itself. Specifically, this means that the Buddha and all living beings are not separate; the buddha realm does not exist apart from oneself. Nichiren explains this in simple terms: “As to where hell and the Buddha exist: some sūtras say that hell lies beneath the ground, while others say that the Buddha dwells in the west. But close investigation shows that both exist within our five-foot body. For hell is in the heart of a man who despises his father and makes light of his mother, just as flowers and fruit are already present within the lotus seed. What we call ‘buddha’ dwells in our mind, in the same way that stones contain fire and that jewels have value intrinsically.”