An independent set is a subset of vertices in undirected graph G such that no two are connected by an edge. A k-clique of a graph G is a subgraph of k vertices such that every pair is connected by edges. A cut in a graph is a partition of the vertices into two parts A and B. The size of the cut is the number of edges with one end in A and the other in B. A dominating set in a directed graph is a subset of vertices such that every vertex is either in the subset or adjacent to at least one vertex in the subset. A vertex cover in an undirected graph is a set of vertices such that every edge in the graph is adjacent to some vertex in the set. A path in a graph G is a finite sequence of edges in which any two consecutive edges are adjacent, the first edge should begin with the vertex s and the last edge should end with the vertex t. The cost of a path is the sum of the cost of its edges A Hamilton Cycle in a graph is a finite sequence of edges in which any two consecutive edges are adjacent such that by walking through the edges we visit every vertex exactly once and return to the starting vertex. A Traveling Salesperson problem is finding a finite sequence of edges in which any two consecutive edges are adjacent such that by walking through the edges we visit every vertex and return to the starting vertex. An edge cover is a subset of edges such that all vertices are covered by these edges. K-Coloring -The assignment of k colors to the vertices such that no two adjacent vertices have the same color.