Are you sure it's unambiguous? Four way stops have both a "whoever was here first goes" rule and a "we arrived at approximately the same time so the person on the right goes" rule. That alone adds ambiguity, as they're not well defined.
But it gets worse than that, as pedestrians have priority and can break up the established order. If it's "my" turn, but a pedestrian blocks only my way, someone else can rightly cross out of turn, but then once the pedestrian is clear when does it become my turn again?
