गुणोऽर्तिसंयोगाद्योः

गुण is substituted for the final ऋ in the root ऋ (अर्ति) and in those roots ending in ऋ in which the vowel is preceded by a conjunct consonant, when the Passive character यक् or the Benedictive augment यास् follows.
The words ऋतः, यकि and लिङि are understood here. Not so the word श as its anuvritti is impossible. Thus अर्यते, अर्यात्, स्मर्यते and स्मर्यात् ॥ This is an exception to 1.1.5. In सं स्क्रियते and संस्क्रियात् 6.1.135, there is no Guna, either because in स्कृ the augment स् is considered as Bahiranga and therefore asiddha, or because it is considered as no part of (or non-attached to) कृ, and therefore स् कृ is not a root beginning with a conjunct consonant. See however 7.4.10, where in forming संचस्करतुः, स्कृ is considered as a root beginning with a conjunct consonant. See also Mahabhashya on 6.1.135. The यि 7.4.22 is understood here also; the Benedictive affix must begin with य, therefore not here स्वृषीष्ट, ध्वृषीष्ट ॥ The word non-sarvadhatuka is also understood here, the rule does not apply to the Potential, as इयृयात्, there is slu substitution of sap, reduplication, then there is इ substitution in the reduplicate by 7.4.77, then इयङ् by 6.4.78.