What is the fourfold restraint that a Nigaṇṭha bound? Jainism and Buddhism in interaction

At the time of the Buddha, the Jainas are known as practitioners of severe hardships. The Jaina practices of austerities are constantly brought up in Buddhist Suttas. In general, the Jaina are classified by the Buddha as tapassin (one devoted to religious austerities). Taking the passage nigaṇṭho cātu-yāma-saṃvara-saṃvuto hoti. (DN 1: 57) as point of departure, this essay illuminates how the Buddhist envisages the Jaina in terms of religious ideas and practices and how the polemics between these two traditions evolved, contributing our understanding of intellectual trend at the time of the Buddha. The meaning of nigaṇṭho cātu-yāma-saṃvara-saṃvuto hoti has been discussed by many scholars (most recently, see ***Balbir, 2000, Jaini, 2003, Watanabe, 2003 etc.). However, issues raised by this phrase remain elusive as it is a highly figurative expression. To be sure, it is a parody of the Jaina attitude towards this world in punning form. Scholars tend to look for the common elements that these two Samaṇa traditions share. Nonetheless, the profound difference between these two intellectual traditions, under a veneer of similarity, should not be overlooked. Early Jainism and Buddhism are not one tradition marred by negligible discrepancy. Only when the distinctive features of these two religions are accurately assessed, will the gravity of differences be fully appreciated. This issue has not been squarely addressed by scholars and the present exploration attempts to do so.