Necessary.
Gahīnon un immāli hi Buy'a ya unna ituduy atonmi an muntapeng.
It was necessary for Buy'a to come before he could teach us what to do in building the stone wall.
Obligatorily followed by un and a sentence.
Undan gahin un'a mi'gāud an ammūna ami ti ologmi.
It's not at all necessary for you to join in doing spadework; we are enough because we have the ability (to do it without you).