Although it occurs only immediately before selbri, {na} is a wide-scope
negative, that is, its scope is the entire bridi in which it occurs. In
other places, {naku} must be used, but its scope extends only rightward from
its position.
Thus {da na broda} = {naku da broda}={naku su'o da zo'u da broda}={ro da zo'u
naku da broda}= {ro da naku broda}={roda broda naku}