Hacker News Reader

Build an object out of legos and then reconstruct the shape of what you built by only looking at it from the sides and above.

Seems simple enough in many cases. But I think the difference is in the generality of it. Being able to do it for any interior arrangement of parts.

Agreed, that was what I was trying to say. You can build a lego structure that you can not infer by just looking at from the top, bottom and sides.