2 ms·

I think the confusion comes from the formulation of the problem itself. It is incomplete. Here is a task that I think is solvable: - C should be on the ground;

• ColinWright 9y ago
  But part of the point is that in real problems you state what you want, not realising that other things might be necessary. Here it turns out to be necessary that C is on the ground, but that is something that the system should be able to deduce from the goals given. As I've said elsewhere, this is a minimal example of the kind of thing that can be required. This sort of thing can and does occur "in disguise" as a tiny, hidden sub-component of real problems, where you, the human, don't have the luxury of going "Oh, it's obvious what's wrong."