In the chandas (Vedas) the Absolutive iṣṭvīnam is irregularly formed for iṣṭvā,
To the root यज् is added that क्त्वा, and the final आ is replaced by ईनम् ॥ As इष्ट्वीनम् देवान् for इष्ट्वा देवान् ॥ The च in the sutra indicates that there are other forms like this, as पीत्वीनम् for पीत्वा ॥,