因明入正理論疏 2.171

2.171

論　此中常宗，以虛空、極微等為同品，無質礙性，於虛空等有，於極微等無。

Treatise: Here, in the thesis of permanence, space, atoms, and the like are the homologues; the nature of lacking tangible obstruction is present in space and the like, and absent in atoms and the like.