Vedic - 001 - The Root अस्

अस् - as - to be

Present Indicative
3rd Person: अस्ति स्तस् सन्ति
2nd Person: असि स्थस् स्थ
1st Person: अस्मि स्वस् स्मसि

Optative
1st person: स्याम् - May I ... स्याम - May we all

Imperative
3rd Person: अस्तु - May it be सन्तु - May it all be

RV 10.40.6
युवं कवी स्थः -> yuvaM kavI sthaH -> You two / sages/ are -> You two are sages.

RV 1.98.3
तव तत् सत्यम् अस्तु -> tava tat satyam astu -> of you/ it/ true/ may (it) be -> May it be true of you

Source: http://www.utexas.edu/cola/centers/lrc/general/facultyhomes/karen.html