The game is great, but at the last level I found that there *was* some mandatory guessing.
I found myself with three galaxy clusters accounted for, and a small area that was closed down by the clusters. I could guess that there should be a fourth cluster, given that each level had more clusters than the previous one; plus the interface allows for four cluster boxes. But nothing was explicitely telling me to watch out for that!
Still very glad of the little time I spent on here. :-)