Traveling Salesperson Problem (TSP) and thousands of other problems are equally hard in the sense that: if we had an efficient algorithm for one of themwe could have efficient algorithms for all of themsuch an algorithm has never been found, but it’s never been proven that one is not possiblethese problems are called NP-completeA problem for which an efficient algorithm is not possible is said to be “intractable.”Section 9.1: IntractabilitySection 9.2: Input Size RevisitedSection 9.3: Three General Problem CategoriesSection 9.4: The Theory of NPSection 9.5: Handling NP-hard Problems