The affix aṅ is used in the chandas (Vedas) when the affixes of the āśīrliṅ (Benedictive) follow.,
This debars शप्. The affixes of the Benedictive are ardhadhatuka by 3.4.116; but in the Vedas they are sarvadhatuka as well; see Rule 3.4.117. The scope of the present rule is confined to the Benedictive of the verbs स्था, गा, गम्, वच्, वद्, शक् and रुह्; as उपस्थेयम्; सत्यमुपगेयम्; गमेम जानतो गृहान्, मन्त्र वोचेमाग्नये, विदेयमेनां मनसि प्रविष्ठां; व्रतम् चरिष्यामि तच्छकेयम्; स्वर्गं लोकमारुहेयम्.
The affix अक् is employed in the Chhandas after the verb दृश् in the Benedictive. Had there been अङ्, it would have caused guna by rule (VII. 4. 16.); to prevent this, अक् is ordained; as पितरञ्च दृशेयं मातरञ्च 'May I see the father and the mother'.,