In the chandas (Vedas) are found the irregular forms 1. babhūtha 2. ātatantha 3. jagṛmbha 4. and 5. vavartha,
As त्वं हि होता प्रथमो बभूथ (= बभूविथ); येनान्तरिक्षभुर्वाततन्थ (= आतेनिथ), जगृम्भा ते दक्षिणमिन्द्र हस्तम् (= जगृहिम), ववर्थ त्वं हि ज्योतिषा (= ववरिथ). See 7.2.13. This is also a niyama rule with regard to वृ for by 7.2.13 the root वृ was already anit, and its Perfect would have been ववर्थ by that rule. The special mention of this form shows that in secular literature this root is always सेट् before थ of the Perfect.,