3.This exercise considers the implementation of search algorithms in Prolog. Suppose that successor(X, Y) is true when state Y is a successor of state X; and that goal(X) is true when X is a goal state. Write a definition for solve(X, P), which means that P is a path (list of states) beginning with X, ending in a goal state, and consisting of a sequence of legal steps as defined by {\tt successor}. You will find that depth-first search is the easiest way to do this. How easy would it be to add heuristic search control