1) Being essential or indispensable.
Bâyesté, p.p. of bây-, bâyestan "to be necessary," from Mid.Pers. abây-, abâyistan "to be necessary" (abâyišn "necessity," abâyišnig "necessary"), from Proto-Ir. *upa-aya- "to reach," from upa-, → hypo-, + ay- "to go, to come," → precession.
necessary and sufficient conditions
butârhâ-ye bâyesté o basandé
Fr.: conditions nécessaire et suffisante
If event A must occur for event B to occur, then it is said that A is → necessary for B. If event A may cause B but there could be some other cause as well, then it is said that A is sufficient to cause B. See also → if and only if (iff).
Fr.: vérité nécessaire