Māṇḍūkī Śikṣā 125

125

caturthaṃ tu tṛtīyena dvitīyaṃ prathamena na tu
ādyamantyaṃ tṛtīyaṃ ca svākṣareṇaiva pīḍayet

The fourth [is doubled] by the third, the second by the first, but not [by itself]; / one should compress the first, the last, and the third by its own syllable alone.