Oh? At least in Germany it's that you have to yield to a driver to the right (ignoring priority roads) but if you have an intersection of non-priority roads and a car from each direction someone has to make a decision to go first, otherwise it's a deadlock.
Europe doesn't generally use 4-way stop signs (http://en.wikipedia.org/wiki/All-way_stop) in the traffic regulations; intersections tend to be either regulated, or with one road designated as the priority, or as roundabouts, not like this.
I've driven a bit around Europe, but I have never seen a single such intersection in my life - if they exist, they must be rare.
Of course, "if you have an intersection of non-priority roads and a car from each direction" then it's the same, but in practice it seems that 'they' make sure that such intersections are only in extremely low-traffic places where you'll very rarely see another car at the same time.
In Sweden as soon as you're in a residential area or out in the countryside, unmarked priority-to-the-right crossings are the norm. And if cars from all directions in a crossing arrive at once, you end up with an ambiguous 4-way stop situation.
In creating an autonomous car, successfully handling those rare edge cases are going to be the thing that differentiates success from failure. Roundabouts and Michigan left turns are rare in most places in the US, but an autonomous car would still have to be able to handle them.
Unless I misunderstood the problem.