जॄ-व्रश्च्योः क्त्वि

As जरित्वा or जरीत्वा, 7.2.38 and व्रश्चित्वा ॥ जॄ was prohibited by 7.2.11. and व्रश्च would have been optionally सेट्, as it has an indicatory long ऊ, by 7.2.44. Hence this rule. The special mention of ktva, stops the anuvritti of kta and ktavatu.,