Where two opposite things are equal in that neither one superior to the other, and yet neither are the same (since equal is literally the same/has to be the same thing for them to be equal).
It's almost like male lives are cheaper than female lives since there are double standards in what females are allowed to do to all sexes, and yet not all sexes can do them in return to females. Kind of like having universal donor and universal recipient blood types, it's one-sided and not duality.