妙法蓮華經玄贊 4.62

4.62

Śaṅkha appears when the kalpa increases, and because his life is long he meets Maitreya; it is not that Maitreya Buddha appears when the kalpa is not decreasing. Furthermore, if a buddha does not leave the household life, he ought to assume the position of a golden-wheel king, but he does not definitely do so. The meaning is the same for the eight sons of Candrasūryapradīpa; because those were reward bodies, there is no such fault. This applies to the golden-wheel kings who must appear when the kalpa increases; the times when silver-, copper-, and iron-wheel kings appear are not fixed. Therefore, King Aśoka in the era one hundred years after the Buddha's nirvāṇa was an iron-wheel king.