Mimamsasutra 42.2.11-3

42.2.11-3

brūmaḥ- ’anyā anyā ṛco bhavanti, tadeva sāma’ ityṛcāmanyatvamatra varṇyate| tacca pādapragrathane saṃbhavati| ṛkpragrathane tu yeyamṛkpūrvasya tṛcasyāntyā, saivottarasya tṛcasyā''dyā, ityanyatvamṛco na syāt| tasmāt- pādasya pragrathanam ||

we reply: "Different and different verses occur, [yet] the sāman is the very same"—thus anotherness of verses is described here. And that is possible upon the interweaving of quarters. But in the interweaving of verses, the verse that is the final verse of the previous triplet would be the first verse of the subsequent triplet, so there would be no anotherness of the verse. Therefore, the interweaving is of quarters.