What word can fill in the blanks in the following pair of analogous sentences?
If B is necessary to A, then A depends on B and A is dependent.
If B is necessary to A, then B __________ A and B is _________.
Is there a word, the opposite of "dependent", meaning "is depended on"?
Edit: 'requisite' fits the second blank:
If B is necessary to A, then B __________ A and B is requisite.
I don't know a form of 'requisite' that can fill the first.