The affix śyan is optionally used after the root akṣ 'to pervade' when it is preceded by the preposition sam and when a sārvadhātuka affix denoting an agent, follows. ,
Thus अक्ष्णोति or अक्षति 'he pervades or obtains'.,
अक्षो ऽन्यतरस्याम्
Adhyāya 3 · Pāda 1 · Rule 75