Suppose Inventor One invents and patents a new and useful rocket launcher. Inventor Two then comes up with a new and useful improvement on the invention. Inventor Two is entitled to a patent on the improvement (assuming, as always, that she meets the other requirements of patentability). Inventor one owns the patent on the rocket launcher, and Inventor Two owns the patent on the improvement. Who could make, use, sell, offer to sell, and import the improved version of the rocket launcher, without infringing either patent?