"Bossaerts et al. compare a patent system with a market reward system in an interesting experimental setting. The innovation is the solution to a combinatorial problem called the knapsack problem. In the knapsack problem there are Z items each with a certain value. You must choose which items to put into the knapsack in order to maximize it's value but each item also has a weight and you cannot go over a fixed weight which is set such that you can't carry all the items. The solution to a knapsack problem is not obvious since it's not always best to include the most valuable items. The authors argue that solving the knapsack problem is like combining ideas to create a new innovation. The authors, of course, know the optimal solution to each knapsack problem."