In real world of two dimensions there are no particles in the way you mean.The quiz is about 2-dimentional world..
My solution is that, inner disk will be isolated first, because real world consist of particles, even photons.
In the 3 pictures A, B and C, we see the circle is approaching closure.. the question:
will the circle (the black line) completes first, or the yellow pie inside will be completely isolated from the outside world first?
Yes Luca, the question is exactly about this. So you think the two events occur at the same time.. the absolute same time..The "inside part" will be an "inside part" just when the circle will be completed!
No (I am not an expert yet...)ps: @@derez , citing the cucumber are you claiming the chairmanship to the pervert circle?