唯識二十論述記 2.51

2.51

The Commentary says: This explains the reason that aggregate form has the extent of a paramāṇu: because each of the six [surrounding ones] mutually faces [the center], their extents do not exceed one another; hence all aggregate form has the extent of a paramāṇu. An anumāna should be formulated: 'Your aggregate forms should have the extent of a paramāṇu; because their extents do not exceed a paramāṇu; just like a single paramāṇu.' Alternatively, an anumāna can also be formulated based on the verse: 'The extent of your aggregate form should be like a paramāṇu; because it occupies the same location as a paramāṇu; just like a paramāṇu,' being identical without difference. However, the phrase 'like a paramāṇu' in the following verse applies both as the predicate of the pratijñā and as the sādharmya-dṛṣṭānta, because its meaning does not conflict [with either]; or it is only the predicate and not the sādharmya-dṛṣṭānta, because the momentum of the text is different. Its pratijñā, hetu, and so forth should be matched accordingly according to the meaning.