«لَا هُنَّ حِلٌّ لَهُمْ وَلَا هُمْ يَحِلُّونَ لَهُنَّ»
Those women are not lawful for those men, nor are those men lawful for those women.
In the first clause hunna is the subject of the judgment and lahum marks the related party. In the second, hum becomes the subject and lahunna marks the other party. The direction of the predication and its attachment has been reversed.
Thus ʿaks is not limited to exchanging adjacent nouns; it can reverse syntactic and semantic relations across whole clauses.