The s of the first person is optionally elided in the leṭ (Vedic Subjunctive).,
As करवाव or करवावः, करवाम or करवामः । The first person is used in the sutra to indicate that the स् is not elided in any other person.,
स उत्तमस्य
Adhyāya 3 · Pāda 4 · Rule 98