sarcu -sa'u- gismu

x1 (abstract) is necessary/required for continuing state/process x2 under conditions x3.

Also factually necessary, necessity, prerequisite, condition, precondition. See also cmavo list sau, nitcu.

In definition:

sau
sarcu modal, 1st place requiring ...
sesau
sarcu modal, 2nd place (process) necessarily; necessary for ...
tesau
sarcu modal, 3rd place (conditions 2) necessarily; necessarily under ...

In notes:

nitcu
x1 needs/requires/is dependent on/[wants] necessity x2 for purpose/action/stage of process x3.