Legal estoppel is a doctrine that prevents a patent owner from licensing one patent, only to make that license worthless by enforcing another patent. The idea here is to prevent the licensor from taking back that for which he already received consideration. For example, suppose an inventor obtained two patents, a broad patent covering a new mousetrap design, and a narrow patent covering a one specific variation of the design. Further suppose a mousetrap within the scope of the narrower patent would necessarily fall within the scope of the broader patent. In this situation, if a party acquired an express license to practice the narrower patent, that party would likely also receive an implied license to the broader patent as well under the principle of legal estoppel. Put differently, the patent holder would be legally estopped (prevented) from asserting an infringement claim against the licensee of the narrower patent.