仁王護國般若波羅蜜多經疏 2.30

2.30

The commentary states: As for "emptiness of emptiness," it means that all phenomena are empty, and this emptiness is empty through emptiness. As for "great emptiness," it refers to the ten directions: east, south, west, north, the four intermediate directions, above, and below. Here, the east is empty through the east, and the south and others are also like this. As for "ultimate emptiness," "ultimate" refers to nirvāṇa; this ultimate is empty through the ultimate, because two are conventional and one is real, and their characteristics and natures are empty. Next is the third [part], the emptiness of the conditioned and unconditioned.