अतो येयः

After a Present अङ्ग (stem) ending in a short अ , इय् is substituted for the सार्वधातुक या (i.e. for the या of the augment यास् of the लिङ् (Potential)).
Thus पचेत्, पचेताम् and पचेयुः ॥ The य् of इय् is elided before affixes beginning with a consonant by 6.1.66. In the case of पचेयुः, the pararupa of 6.1.96 is prevented. Why 'ending in a short अ'? Observe चिनुयात्, सुनुयात् ॥ Why 'short'? Observe यायात् ॥ Why sarvadhatuka? Observe चिकीर्ष्यात् ॥

The objector may say, the form चिकीर्ष्यात् will be so by the elision of अ under 6.4.48, and so there is no necessity of reading the anuvritti of sarvadhatuka in this sutra; for when अ is elided by अतोलोपः 6.4.48, in the case of ardhadhatuka या the present rule cannot apply, as there is no base left which ends in अ ॥ To this we reply, this is not a good reason: for then in the case of पचेत् and यजेत् also, the rule अतो दीर्घो यञि 7.3.101 would apply, and the अ of पच would require to be lengthened. But that is not so. The fact is that the present sutra debars rule 7.3.101. Therefore, as this इय् substitute debars the lengthening of 7.3.101, so it would debar the lopa of 6.4.48. Therefore, if the anuvritti of sarvadhatuka be not read into this sutra, the इय् substitute would apply to ardhadhatuka also, and the lopa-elision 6.4.48 would not help, as that would be superseded by this special rule. Therefore the anuvritti of "sarvadhatuka" should be read into this sutra.

The above is stated on general grounds. But if the maxim मध्येऽपवादाः पूर्वान् विधीन् बाधन्ते नोत्तरान् (Apavadas that are surrounded by the rules which teach operations that have to be superseded by the apavada operations, supersede only those rules that precede, not those that follow them) be applied here, then the present sutra would supersede only the preceding sutra 6.4.48 and not the following sutra 7.3.101 for which would not be superseded by the present sutra. In this view also, the lopa being superseded at all events, the anuvritti of 'Sarvadhatuka' must be read into this sutra.

In the दीर्घ rule 7.3.101, the word 'sarvadhatuka' is understood from 7.3.95. But according to some, the word तिङि of 7.3.88 is also understood there, so that they would lengthen the अ, before a sarvadhatuka personal termination (तिङ्) only, and not before every sarvadhatuka affix in general. According to this view, the present sutra will debar only the dirgha rule 7.3.101 and not the lopa rule 6.4.48, on the maxim येन न प्राप्ति &c.

The word येयः in the sutra is formed by या + इयः; and या is exhibited without any case-termination. Others say, the word is यः the sixth case of या formed on the analogy of विश्वपः by the elision of आ 6.4.140. Then यः + इयः = य + इयः 8.3.19 after this elision, there ordinarily would take place no sandhi; as this elision is considered asiddha 8.2.1 for the purposes of 6.1.87. Contrary to this general rule, however, the sandhi takes place here and we have येयः by 6.1.87. The अ in इयः is for the sake of pronunciation only. The real substitute is इय् ॥

Some read the sutra as अतो यासियः ॥ So that the sthani is यास् and not या, and यासियः is a genitive compound.