Prime Graphs: There are some efficent algorithms for restricted set of graphs for NP hard problems. It gives me the intuition that there are core graph of those restricted set which divides all elements in their set (Altough division is not defined yet). In this sense there exist an algorithm which solves this restricted set efficiently by solving its core problem. These core's are called prime graphs which is analogous to prime numbers where prime number has their unique divisors. Division means that there is polynomial algorithm that can convert problem into solution or core problem. To solve those prime graphs an machine need to be started to solve and store them. Then anyone who needs a solution to their problem need to find a conversion to prime graph and query from already solved graphs. This is different from polynomial time conversion from one problem type to another. This time the iteration held on graphs as similar to numbers.