The prohibition and the augment ordained by na yvābhyāṃ padāntābhyām pūrvau tu tābhyāmaic [[7.3.3]], do not apply to a word which expresses the reciprocity of an action.,
As व्यावक्रोशी, व्यावलेखी, व्याववर्त्ती, व्यावहासी ॥ See 3.3.43 and 5.4.14.,
न कर्मव्यतिहारे
Adhyāya 7 · Pāda 3 · Rule 6